The calculations are done in VA, not amps
The first issue with your numbers is that 30A campers only use 120V, while 50A campers get 240V. This means you have to do your load calculation in VA, with the 50A camper getting 12000VA and the 30A campers getting 3600VA each, as per NEC 551.73(A), for a baseline total load of 12000 + 3600*3 = 22800VA. However, 551.73(B) also permits a demand factor from its associated table to be applied; since you have 4 sites, this specifies a 75% demand factor to be taken of the calculated baseline total, for a final load number of 17100VA, or 71.25A @ 240VAC.
Fat aluminum is your friend here
For this level of current, I would recommend you use 2-2-2-4 Al mobile home feeder cable instead of copper wire if at all possible; it can handle 90A when landed on the 75°C terminations found in modern distribution equipment, and is far cheaper per-foot than the equivalent copper wire, in addition to being available as a commodity product.
Running it in a 1½" or 2" PVC conduit is preferable since it leaves room for later wiring upgrades, although one can forego that if conduit's not an option for some reason. The subpanel breaker will be 90A for most modern panel types, as well.