cant...with my '08 Tundra 5.7 4X4 I tow an '11 Keystone Outback rated 6,000 dry and a 1K/10K Equalizer. My tongue wt. with full 30 gals. of fresh water in the tank at the rearend, 2 #30 full propanes and a group 27 battery on the tongue, it's 760 lbs. Add the Equalizer hitch head (guess about 40) and a few clothes and the food stock in the fridge and cabinets I'm probably close to 1,000.
Payload in the truck is the DW and I, a 18 lb. Sheltie and maybe 300 lbs. cargo.
Your dad should have NO problem. A year ago we took route 7 through the Ouachita Mountains Arkansas (LOTS of 25-30 mph switchbacks) with no sweat.
As far as getting a tongue weight, I went to one of the local RV places (US Adventure), was real polite with the service mgr. and he helped me get my tongue weight with his scale. ;)