Hi and welcome to Pet Talk.

Sounds like Franklin is in serious need of a diet. Poor guy. It's not healthy for him to be that big. I really don't have a suggestion as to what would be best. Since you have treated him for fleas now and don't actually see any fleas on him I would be concerned that he may have a different problem.

Could you call your vet and ask if it could possibly be anything else besides fleas? I'm guessing the owner didn't say he had a skin condition or anything.

Good luck, I'm sure someone else here will have a good idea.