I have two lettuce nudis that do pretty well in my 75. I would say they are pretty hardy, as one took a trip around my vortech and got a pretty good gash in him. After about a week of not seeing him, he appeared and was back at it again. Aside from that and the occasional trip down the overflow, I find them fascinating!
The main thing with these guys is to have a food source for them. They will devour virtually any type of algae in your tank, but I have had no luck feeding them nori during an absence of visible algae. That said, I don't clean the back glass often, that way they have a "go to" spot.