If you're considering an RV that will see heavy use (full-time or seasonal), I'd be leery of "lite" 5th wheels. Although there are ways to make a strong, durable, light 5th wheel (lightweight, high strength composite materials, extensive use of aluminum - think aircraft type construction), these tend to be pricey because of the material costs and technology required. Unfortunately, it's cheaper to build a "lite" RV by cutting frame and running gear size, floor, wall and roof thickness, particle board (versus real wood) cabinetry, etc. This construction may be somewhat sufficient for weekenders or vacation RVers, but generally won't stand up well under heavy usage. That's why true "full-time" 5th wheels are as heavy as they are.
Having said that, I've seen individuals full-time in tents and slide-in campers, so I guess anything's possible if one is willing to deal with the negatives.
Rusty