Vault tunnel?
Eh, maybe but I doubt it. There's pretty good support for double-tac here, the opponent can start picking up Bazaars and more Swindlers and kinda ruin your day. The only thing that makes me hesitant about double-tac is the weak trashing (do you even bother with Develop?) and not-so-great draw.
I really disagree with this. Vault/Tunnel is very resilient to Swindler (in relative terms) - hitting the actual card Vault hurts it a lot, the rest, much less than in most any deck. Of course, Swindler is a pretty good card in general anyway. But beyond this, Double Tac doesn't have very good support at all - you absolutely would need to go Develop, because there's just no draw beyond Tactician, which means you're limited to 10 card hands. 10 is a lot, but you are adding at least a couple swindlers and your two tacticians, and eventually green cards (I am not counting Bazaars since you get to flip them into another card). You will have 4 or more non-drawing cards you want to add very easily - and that means missing playing the 2nd tactician 30% of the time already. Your deck isn't reliable. Even with Develop, it's going to be slow in getting to reliability. Furthermore, what's the payoff? I play 4 bazaars and 2 swindlers to get $8? It seems like a lot of work for not so much upside.
Vault is a premier BM enabler (in the absence of discard attacks, which really hurt it), and Tunnel helps... some. I don't actually think it helps a ton, but hey, it's something.
There's other options here though. FG/BM is also quite nice - with Nomad Camp, this probably takes out Vault/Tunnel in a BM mirror? Unless that contests FG? I don't know, it's very tricky. I imagine how the game plays out is probably actually more important than 'strategy'. I would probably go Swindler/Silver, getting more Swindlers if they go FG, and otherwise/generally focusing on Vault.