In stead of running around in circles trying this and that. Just buy a 3/4-1 ton truck. Then you will be able to tow just about anything that meets your needs. Then you can get any size TT or most 5th wheels you want. When you start analyzing the situation too much then it all gets confusing. What your doing is what most newbies do and that's to try and tow the most with the least. They all end up trading up for a bigger truck. IMO if your full timing you need something fairly large. Even a 30' 5th wheel will be too much for a 1/2 ton when full timing. Most guys that tow 5th wheels with 1/2 tons usually say they travel lite. You won't be traveling light full timing.