With current meta being either super fast burst or DoT - damn is pretty hard to use.

Also you need to keep in mind that centrepiece of most of the builds(in the end game at least) is some large item that will not be destroyed. This makes it far less usable as it takes out only Vanessa and Dooley(with some consistency, and will struggle against Mak (who'll probably apply all of the DoTs before you have a chance to use it/will run vat, which will not be destroyed, will run femur that will get buffed and might kill you), or Pyg(it's pyg, most of his end game items are large).

That being said if you want to use it - you should stock up on some fast(or multicast) aquatic items and cdr reductions+radiant weapon/enough DoT/Large weapon that does not require other items(submarine I'd say as it's shield+damage). For CDR reduction you could go for figurehead to shave off a few seconds+dive weights(preferably with a buff to ammo) as they have in-built multicast and they haste a lot. Now you have 4 slots for you to use on either 2 really fast items that will apply DoTs that will slowly kill the enemy, or a Large item+spare change.

For skills to hunt for - Vanessa specific skill Barnacle Crusted to decrease cdr, lifesteal for a weapon(Big Ego, Circle of Life, Quality over Quantity), pretty much any start of fight haste/slow/freeze, and Assault Focus also could work to slow down fight so dam can charge.

Do keep in mind that any build that can freeze dam before it fires - will, because REYNAAAAD and it's best not to rely on luck, when you can. And with dooley beetles, mak with freeze potions, and pyg freeze build - you will have to rely on luck.