Several tips about The Wall from a newbie:
1. CORNERSHOOT! Get as many shotgun shells as you're able to. Wreck the Wall somewhere at the top just to make them start pouring out. Radar scout with shotgun (this means, shoot into the darkness and listen if hit something - even a single hit will result in 1 damage and an angry ROAR), and back out to the point where you can cornershoot anything that will get out. The trouble is if you will end up with more than two B's getting at you, this way they will squeeze themselves out of the wall you're hugging, and the more distant B will have a line of fire at you - then duck and abandon this corner, and start run-and-gun, thankfully shotguns always hit.
2. Also, if you have a spare rocket, make a dent at another place in the Wall (not a whole passage, but merely a 1-tile dent) to have a backup cornershoot position to retreat to.
3. Use combat shotgun or plain shotgun to cornershoot, but if the B's will come as close as here:
..B...
####@.
aka knight's move from you, have a DS ready (if you have one of course) and blast at them, they will likely fly 3-4 squares back or die. (Speaking about V's there, I yet have to play normal game on UV to tackle The Wall).
4. You can cornershoot with other weapons than shotgun, but they will have a big chance to miss. So bring a pistol alongside yourself in case of not having enough shells, to plink at then barons while they are barely visible while you're hugging the wall. You can aim at a baron of hell if you know where it stands (or predict its movement if it's coming at you, if you don't have Int2) by pressing "f" and targetting a desired square manually. Tedious, but doable.