I would keep you snakes setup how it is except I would add a bit of constuction paper on the sides so its not as open. Other then that I dont see any problems. I stated with a 20g L tank for my first and second snakes (seperate tanks) and never had any issues. Its all dependent on the snake. If your snake eats, poops, and sheds fine then leave it be.
I agree on the covering the sides thing. If you use a thicker material, such as foam board, you can insulate the tank a little bit if that's ever an issue.