Hello. I have recently started to take a liking to red shops. Goblin Welder is one of my favorite cards. Here is my current list.

// Vintage Uba Shops

// 60 Maindeck
// 31 Artifact
1 Black Lotus
1 Mox Emerald
1 Mox Jet
1 Mox Pearl
1 Mox Ruby
1 Mox Sapphire
1 Sol Ring
1 Trinisphere
1 Chalice of the Void
4 Sphere of Resistance
4 Null Rod
4 Crucible of Worlds
4 Smokestack
1 Mana Vault
4 Uba Mask
1 Mana Crypt

// 8 Creature
4 Goblin Welder
3 Sundering Titan
1 Lodestone Golem

// 21 Land
4 Mishra's Workshop
4 Bazaar of Baghdad
4 Barbarian Ring
3 Mountain
4 Wasteland
1 Strip Mine
1 Tolarian Academy

// 15 Sideboard
// 8 Artifact
SB: 4 Ensnaring Bridge
SB: 4 Tormod's Crypt

// 3 Land
SB: 3 The Tabernacle at Pendrell Vale

// 4 Sorcery
SB: 4 Shattering Spree

Some things I am thinking about are if I should maindeck Thorn of Amethyst or not. If I did, I may replace Uba Mask. Uba mask is great with Bazaar, but sometimes I feel like 4 spheres maindeck is not enough, and I need 8. Opinions?

I think dropping a bazaar and a b.ring for 2 ancient tombs would be beneficial. It allows you to cast your lock pieces easier.

4 Null Rods, 4 Uba and 4 crucible feels like over kill. I would look to drop at least 1 of each. This would allow you to play Tangle wire. However, with everyone wanting to use the attack phase you could play Bridges.

I fully agree with the preceeding post.

Here is a link to a quite similar old list of mine (the meta was different so it would need some adjustments)
Uba Mask

To answer your question, if your meta is combo heavy i would put 3 sphere/thorn in the SB and use 4 in the main.

I would also use different robots : keep only 1 sundering titan and use instead of the others wurmcoil, and/or masticore and/or duplicant (triskel and karn are great too but not very friendly with null rod).

I don't see a single strategic reason to play Uba Mask/Welder; The format plays 3+ Swords to Plowshares and 3+ Mental Misstep on top of other artifact hate and Uba Stax has traditionally crutched on Goblin Welder HARD.

@Soly I agree with you. Unfortunately Goblin Welder is one of my favorite cards, and "red shops" is probably the best "goblin" deck in vintage. I'm a sucker for tribes (play elves in legacy and merfolk in modern), so this is more for my personal enjoyment.

@Soly i agree that it may not be the best choice in the current meta (MUD would be more direct and efficient for exemple) but IMHO it is not as bad as you say :

• lightning bolt that was played some years ago was far worse since it could ping us too. In those days i managed to get some nice results with that kind of welder build, bolt/sword/decay are trouble some and make it more difficult but not impossible.
• if people decide not to side out mental misstep i can only thank them silently because they could have bring in far worse.
  To elaborate a bit, welder is important but some other plays are much more crucial in the beginning of the game. It is also possible to use cavern and actually there will be some games where one won't see welders so the deck must be able to work without it. There are several build choices dépending on the meta but the central card of the deck is not welder but tangle wire (that will be used either as a tempo or a control card depending when in the game). I have been playing 3 ensnaring bridge in the main for several years and i can't remember how many games i won just because of it.

MUD, dredge and to some extend Eldrazi are very good matchup, Oath is less bad than with MUD, Gush/mentor matchup is really tricky and skill intensive and not favorable i would say, combo (Paradox) will depends a lot on the toss.
So not the best choice in the current meta but it is very fun to play and many players don't know how to play against it. For me, it is fair enough.

Edit : chalice restriction was a huge hurt for STAX, here is a reason i can hear about this deck not being a good choice. Control shop was really hurt and so far i see nothing in the new sets that can help it.

All of this information I am about to provide is somewhat dated and may not apply to the current meta, but I played a lot of Uba Stax back in the day. Here are some comments:

The real strength of Uba Stax is not Welder. It is Workshop. There are two kinds of hands that are keepable. There are Workshop hands and there are Welder + Bazaar hands. Everything else is pretty bad. The problem with Welder + Bazaar hands was already addressed by Soly. You are leaning hard on a 1cc 1 toughness creature that doesn't do anything the turn it comes into play. In many metas this is a huge no-no.
Uba Stax should not be thought of as being built around Welder. Welder is a nice like to have card. It is something that costs you 1 mana and your opponent must answer it. It is not a card to build your whole strategy around.

The best card that your list is missing IMHO is Serum Powder.

Serum Powder allows you to aggressively mulligan to a hand with Mishra's Workshop or Sol Ring. You do not do this quite as aggressively as Dredge mulligans for Bazaar, but you should mulligan a lot.

General advantages of Serum Powder in Uba Stax are:

1. It is a free one sided draw7 that can be played on turn 0. (AKA it is just a good card in general)
2. Tapping for 1 mana is actually really good. Opening up with turn 1 Mox, Shop, Powder, Resistor is usually a strong play as you can play pretty much any card in your deck through Resistor the following turn.
3. The 3cc mana cost is totally doable.
4. The fact that it is a near dead draw in the mid/late game is heavily mitigated by Bazaar. Just pitch it to Bazaar.
5. It Welds out for better artifacts.
6. It Sacks to Smokestack.
7. It taps to Tangle Wire (if you play it)
8. Karn turns it into a 3/3 beatstick.

A big disadvantage is that it is shut off by Null Rod.

Null Rod is a really good card. We had a long debate once about the pros/cons of running Null Rod. I remember I was initially against it, but warmed to it as the debate went on. Now that Chalice of the Void is restricted that makes Null Rod better in a few ways. Chalice@0 already shut off Moxen, so Rod was weaker. Chalice@2 shut off Rod.

What I did not like about Rod was that it would shut off these artifacts that my opponent would either be sacking to smokestack or tapping to Tangle Wire anyway. Also Null Rod shut off a bunch of my own artifacts (including additional Null Rods) so I thought it was hurting me nearly as much as it hurt my opponent.

As I mentioned earlier the key to Uba Stax is the Shop and not Welder. For that reason I am against Sundering Titan. At 8cc it is significantly harder to cast than other options. I used Karn, Silver Golem back in the day. I did not use Null Rod at the time, but Karn was a fast clock when I needed it, ate Moxen and was much easier to hardcast at 5cc.

I remember concluding that Mana Vault was not that great and that was without Null Rod in the deck.

Consider cutting Null Rod. This might be a TERRIBLE idea now that you can only run 1 Chalice of the Void, but at least explore it. I want to be clear that I am not suggesting you actually do it. Only consider it.

Also consider adding Serum Powder. This only works if you mulligan aggressively to Workshop.

I would recommend dropping Sundering Titan.

Other cards to consider:
Expedition Map: Finds Bazaar, Workshop, Strip Mine, Academy or Barbarian Ring. Note that if you run Serum Powders the 2cc activate cost becomes much easier to cast.

Null Brooch: This combos well with Ensnaring Bridge, Uba Mask and Bazaar. Each tends to empty your hand anyway.

Thank you for all the help! Y'all are a great crowd.

Would thorn of amythest or uba mask be better in this current meta? I originally had mask because it shut down draw, but with PO storm picking up steam, I may go to 4 thorns maindeck on top of the spheres and drop mask.

@Naixin The problem with Mask is that it can get abused by Dack Fayden, and doesnt actually hinder their storm turn.

@vaughnbros that actually makes a lot of sense. Maybe thorn is the better choice.