brimstone man has better chances of being completed with elementalists that get -fire at lvl 6 and have good amount of frost bolt castings. All the rest is up to you man, just hope the first level isn't filled with demons and grues and you can get some safe leveling there. Food preservation is nice to have, you would want that for increased chances of fire resistant corpses.
Trolls might be another very nice option for this challenge. Candle born troll would very much help to offset the fire damage in the tower.
Lvl 50 Dark Elf Mindcrafter.
Lvl 50 High Elf Assassin (Dual weilding).
Lvl 50 Dark Elf Paladin.
Lvl 50 Gnomish Assassin (Failed ultra turned normal gate closer)
Lvl 50 Hurthling Thief (ULE).