Hi there! First of all, I would like to say isopods should not be able to get out of your tank. A lot of that would depend on if you have decorations that lead to the top, and what kind of lid you have. If you have a glass lid, they won't be able to get out. If they were to get out, the likelihood of them surviving is very minimal. They need humidity just like hermit crabs.
MORE IMPORTANTLY...if you do decide to get them...LESS IS MORE!!! LOL!! In my experience isopods have overpopulated all of my crabitats. I'm busting at the seams with them. I do offer them for free. You just have to pay priority shipping because they are live creatures. Basically mine are powder blues and lottery mix isopods.