RV parks are intended for RVs - not for EV charging.
Some parks will place restrictions on the types of RVs that are allowed - Class A (bus size), Class B (minivan size), Class C, travel trailer or 5th wheel. Some parks will not allow RVs older than 10 years. Some parks have places reserved for tents - others won't allow any tent camping. Some parks have places for people to stay without an RV or tent (cabin, cottage, stationary RV, ...).
It's understandable RV parks would limit or prohibit EVs from charging. Unlike superchargers, it could be many hours for an EV to recharge. Staying inside an EV is not like being in an RV or tent - you don't have a bathroom, kitchen or any living area - unless you are bringing your own travel trailer or tent. And that could be viewed negatively by the other customers who area staying at the park in their RVs or tents.
When we purchased our first Tesla in Jan 2013 - there weren't any superchargers - so taking road trips required a lot of planning to find specific charging locations - and plan for how long we would need to spend at each spot. Fortunately, at least for Tesla owners, the situation is much better now - with the supercharger network, destination chargers, and public chargers.
When planning a road trip - if there isn't any chargers where you are going - and only an RV park, then contact them in advance and try to make arrangements to use their power - and find out what restrictions they will place on you. And if they won't allow it, then hunt for an alternative...