I tow a 2015 264BHW with a 2013 F-150 with a 5.0L V8. We have towed in hilly (but not mountainous) areas with no problems, but we can definitely tell the camper is back there. Towing capacity of the truck is around 8,000 pounds.
On some of the steepest hills the transmission drops to 3rd gear, but most of the time it goes no lower than 4th. We average around 11 mpg. The truck has the towing package, so I use the tow/haul mode when pulling the camper. We also have the integrated brake controller.
I personally would not be comfortable towing that camper with your van, given its 6600 pound towing limit. You might be OK on level ground, but you would really be pushing the limits.
2015 Jay Flight SLX 264BHW
2013 Ford F-150