The number you want to find is GCWR - Gross Combined Weight Rating. That's the total of loaded vehicle and anything towed. I suspect yours will be 11,000-11,500 lbs. Then fill up your Navigator with gas, you and DH go to a truck scale and weigh with all aboard. I suspect that will be about 5,500 lbs. That means you have about 5,500-6,000 lbs for your trailer and stuff. That should handle the trailers you're looking at, and usual contents. Our 25' Coachmen TT (4,700# dry) and '02 Ford van weigh just below the 12,000 GCWR loaded for travel. We've towed it 30,000 miles all over the country with no towing issues. Be sure you get a good weight distributing hitch. We have a Reese dual-cam.