Your absolute best bet would be pvc cages from somewhere like Animal Plastics. They hold heat/humidity, are light weight compared to glass tanks, make good displays still, and are easy to clean out. They would cost like $150 a piece though, idk what your budget is. The humidity would warp the wood in a wooden encloaure and allow for mold growth. You could use a rack too, but the kids wouldnt really be able to see anything. What age do you teach? For little kids theyd proabably wanna see things but if it was highschool a rack would be fine bc then you could just pull the snake out whenever you wanna show them something. A rack can be made out of melamine for 3 snakes for like $150. Here is my 7 layer rack i made out of melamine for like $200: