Every vehicle has several ratings which are important to consider. Towing an RV at the tow rating puts most half tons and smaller over 2-3 other of the vehicle ratings, axle ratings, receiver limits, and GVWR.
There are some used 3/4 ton SUVs and full sized vans with the capability for 8000-ish pounds loaded RVs and larger families that have the same value as your $20k Navigator. You do not always have to replace with today's new vehicles at today's new prices. I'll be keeping my eye out for a clean/low mileage 2012-2013 3/4 ton GM SUV as a backup/replacement as we rack up 18k miles per year on our current one.
Renting is highly recommend as a learning process for how your family wants to camp and understanding the vehicle dynamics. That's a great next step!
