A 1500 Series (1/2 ton) PU truck, for towing a 5th wheel.

Manufacturer ratings on trucks are like tent and inflatable boat capacities - A "4 man tent" is really good for 2 or maybe 3 people. A "Half Ton Towable" 5th wheel or TT is probably a good fit for a 3/4 ton and so one. Sure, it's theoretically possible to haul the 5th or TT with a 1/2 ton and stay in within the weight ratings. You'd just better have a separate vehicle driving behind you with your family and gear.