If your toad was actually a trailer that put real weight on the motorhome's hitch, the rule of thumb would be 10% of the trailer's total weight on the hitch (tongue weight). Trailers over a ton can have up to 15% on the tongue and Fifth wheels about 25%. Then you'd evaluate the situation with the GVWR (gross vehicle weight rating) of the coach in mind - maximum allowable weight of the fully loaded coach including cargo and trailer tongue weight. But your truck is not a trailer; its load is entirely on its own axles, none of it on the coach when hitched, and the towbar pivot transfers no weight between vehicles anyway. So don't worry about tongue weight re. your pickup.
What you do need to be concerned with is the load on the coach's engine, transmission, receiver hitch mounts, and brakes. Then you musn't exceed the GCWR, gross combined weight rating - maximum allowable weight of the fully loaded coach including cargo, passengers, and the full weight of whatever you are towing. GVWR, GCWR, Carrying Capacity, and Gross Axle Weight Ratings (GAWR - allowed load on each axle) should be posted inside the coach, usually low on the streetside wall behind the driver's seat and often on a sheet in a closet or cabinet.
Larry indicates his tow hitch is rated at 5000 lbs, but most big coaches I've seen have 10,000 lb hitches like mine. You need to check the tag on yours to find out which it is, because rule #1 is don't pull something that might crack a hitch mount, bolt, or weld, jeopardizing yourself and everyone else on the road with you. On our old gas class A with a 3000 Lb hitch, I could safely tow our old 2600 lb Toyota 4X4, but not our 4500 lb F150 or 3500 lb Explorer. When I checked into beefing up the hitch, no one would do it because the 5000 lb version required bracing that couldn't be applied on that particular coach's chassis framework. No installer wanted to be responsible or ever held liable for such a modification. If you have only a 5000 lb rated receiver on your Patriot, there may be a good reason why Beaver didn't put on a heavier one. Either the framing wasn't there, or the drivetrain and brakes weren't up to the task.
Keeping the cargo load low on the coach just to try and stay under the GCWR when adding your toad, and thinking all is well, is a mistake. The strain on the hitch, brakes, tranny, and engine will still be there. Even if your hitch turns out to be a 10,000 lb unit, 6400 lbs is quite a lot of tow for a 330 HP, and a lot to try and bring to a stop. Adding auxilliary braking will help that, but the strain on the engine, esp. on hills like Larry mentions, will probably be a big issue.
Can the engine handle it? Yeah. Will you be happy with how it handles it? Likely not.
Ford Motor Company usually publishes an annual RV and Trailer Towing Guide which you'd find educational - see if a local dealer has one for you or have Ford send you a copy. General Motors may publish one as well.
;)Joel
