Jayco makes a good unit. I think you are correct on the roof(s) - almost all TT manufacturers are using EPDM rubber roofs, now.
The Jayco model you mention will have about an 800 - 850 lb. tongue weight loaded. With 1/2 ton trucks, the payload capacity is exceeded long before the "towing capacity" (as listed by the truck manufacturer) is reached. I would load the truck with full fuel, people, gear, hitch (I hope you plan on using an equalizer hitch with sway control) and head for the nearest CAT scales. Subtract the scale weight from the GVWR on the door sticker and see what you have left over for tongue weight.
Before going full-time, we towed a 6,000 lb. GVWR TT with a Tahoe with the 5.3. It's a good motor, but would stay at 3,500 RPM for long periods on grades (and that's on interstate highways in the Eastern U.S. with only two of us in the vehicle). This was even more pronounced in the mountains in North Carolina and East Tennessee.
Rob
