You have to use either the Zoo New UTH for hermit crabs or there is another one the Zoo Med UTH item number RH-7. These are the only two you can place on glass and plastic. all others are made for glass tanks. These are the correct size for your five gallon. It has to be on the side of the tank. You should have no issues as long as you song bend the UTH and it adheres flat on the tank.

The Fluker's Clamp Lamp with dimmer is what you want. I don't have any links or images of it. if you look it up you'll easily find it. Almost all Restarts carry this lamp.

You will also want to cover 3 sides of the enclosure with some sort of background to help your frog feel secure and it reduces stress.