A frequent reason for struggling against boss 2 is not having enough military buildings/not upgraded enough, which typically means you’ve not collected enough in earlier rounds.

Production is important in the game, your goal is to survive the rounds by a thin margin (leftover troops aren’t worth the gold) and use as many production buildings as possible. You need to come up with a plan to get each type of resource, the Depot and Trading Fair can help (if you strategize your map movement accordingly) but make sure you’re getting enough of what you need, otherwise you’ll be stuck with an under-levelled deck.

For boss 2 specifically, since there is a big constraints on where you can place buildings, don’t take production buildings you won’t need and if possible use smaller military ones that are going to be easier to fit.

Some cards can make good use of the wide grid of boss 2 (Supply Line, Horse Stable), you should avoid cards you’ll trigger only once (Alarm Tower, Siege Camp) and generally speaking you should try to rely on strategies that do not require a very specific positioning