i do not pug invaders as caster or cleric anymore. most tanks get in there and cannot help but run in. Honestly, i rarely even feel generous and throw up the completed quest either. buffs needed: poison, fire, cold, acid, gh, deathward. nice buffs to have: blur, jump, stoneskin. everything else is a waste. quicken on a cleric is required. sneak for beholders, run for cover when needed. I have been solo'ing invaders for months now, and I have friends who solo on tanks. sounds like to much work for me. effective spells: insta death, banish spells. oh and its nice to have a weapon of some sort when you get tensor's. personally i have dreamspitter (p2p reaver's fate quest)
to be generous, yes one of the OLD ways was to let the tanks go in and tank and raise them when they died.