Thanks for playing!
I think you might have disabled the other trials for testing and forgot about it because I only found fire trials in like 4 runs.
The other trials are available, I think you just got unlucky. Not every floor spawns a shrine room, and shrine rooms always match the dungeon variant they spawn in. The red/fire variant of the Wizard's Dungeon biome always spawns the fire trial room, the purple/electric variant always spawns the electric room, and so on.
Whenever I get set on fire I usually do water + health but if I do that with the barrier upgrade I get neither water nor health and I die.
I think it does heal you, but it doesn't apply the regeneration status that normal healing gives you. I could make it so the barrier status checks for burning and removes it on application.
I think maybe the chem tank upgrades should be given in some other ways because they feel mandatory to get first.
I think it's fine if they're acquired through workbenches, but I agree that the pack upgrades are very, very strong. Especially the increased tank capacity, it makes it so much easier to deal sustained damage. I could buff the player's baseline alchemy stats and nerf the tank upgrades? Do you think that would alleviate the issue?