The aquarium backgrounds are fairly cheap and they attach to the outside of the tank and you can cut them to size. Construction paper or packaging paper works too! Still attached to the outside of the tank.

I attach my vines and leaves through a hole on the screen top so the attachments are outside of the tank. I don't use the suction cups. I tie it with those zip tie thingees for computer cables. I use a pin to untie the zip tie so I can undo it to clean.