Check the Motorhome Magazine Dinghy Guide for 2003 vehicles that can be flat towed, then check the 2003 F150 Owner's Manual under "Towing" to see what's required. If still uncertain, check with a Ford Dealer, or send an email to Service and Customer Support @ Ford.com.
Also, 6500lbs is a bit much for a Class A motorhome - many usually come with a 5,000lb hitch and that's pretty much the limit. Unless you go to a diesel pusher, or a larger gasser with a higher hitch weight rating. A Super C could probably pull it easily, but they're not what you suggest you're in the market for.
