2010 Sierra Scotty HiLander

I'd go with simple math on this one. It is true that the curved sections will reduce the effect, but the math for that is complex as well as marginally significant for your purpose. I'd also definitely err on the side of more car than you need for the simple reasons mentioned above: capacity to go uphill at altitude in summer heat. There is a certain level of terror at finding yourself ascending in the heat and slowing down while watching the temperature gauge on the dash climb toward overheat/cylinder head gasket territory as traffic piles up behind you. You definitely do not want to experience that.

There are actually several factors to consider: tongue weight, car payload, surface area of trailer, car towing capacity among them. Towing a camping trailer is akin to dragging a parachute. Experience has shown that often but not always, car payload turns out to be the deciding factor, but you can't ignore the other factors.