Towed with late1950s sedans. 80-100 HP flathead sixes and eights, then under 4 liter OHV sixes and under 5 liter OHV V8s absurdly over rated at 100-180 HP. Usually with 3 speed manual because the miserable 2-speed automatics wouldn't find the right gear for hills. Eventually had a Hydramatic Olds that might have been great but never towed with it, and my uncle towed with a big old 53 Lincoln.
Nothing had a tow rating. Usually, the TT or camper was lighter than what was towing it, a standard that still works pretty well in Europe.
Trailers were under 4000 pounds, even at 20-22 feet, lighter built and less well equipped. Also, very few high speed highways, 45-50 mph rural speed limits typical, sharing highways with equally underpowered trucks that could seldom reach 50 mph on level ground.
First got started in tents, scouts and family camping, no RV. First step up from carrying everything in the cars and station wagons was a trailer to haul lents and field kitchens, a platoon's worth of field gear. Replaced that with a box truck, late 40s meatpacker's reefer. Let our campsite grow to company size (about 80 scouts in the troop) and added an old schoolbus, ~50 Ford, to the camping fleet. Rattled, leaked cold air, wouldn't go over 50 mpf, but it always got us there.
We live in a different world. It started changing in the mid 1960s, but the idea that you needed a big heavy truck to tow a RV didn't become popular for another 40 years.