I appraised a few RV Parks in my previous career. It's been a couple of years but if you have any specific questions I can try to dredge up some information.
I did a couple that were pretty seasonal and a couple that were in the oil patch in SE New Mexico that were almost 100% full year-round. The latter operated more like a mobile home park than an RV park - though in reality it's pretty much the same business, just less turnover.
Ultimately it all comes down to income. Capitalization rates are pretty high because there's more risk and a fair amount of management involved. It's not as passive as a retail strip mall or office building. As I recall they were generally in the 10-15% range, much higher than retail, office, industrial which would typically be 6-9%. The capitalization rate is simply Net Operating Income / Value.
An RV park generating an NOI of $150,000 that sold for $1,000,000 would be at a 15% capitalization rate. Or put another way, a 6.67x Net Income Multiplier.
As far as financing, you're probably not going to get more than 70-75% loan to value. So if you want to buy that same $1,000,000 property you'll need to bring $250,000 - $300,000 in cash. For a smaller property you might be able to get seller financing with a smaller down payment but probably a higher interest rate or you'll end up paying more for the property.
Keep in mind economies of scale. A 50-pad property and a 150-pad property would both require a single property manager and maybe a second person for maintenance. On the 50-pad property that manager is going to eat up a lot more of your potential profit. On the other hand, you pretty much have to have a full-time manager living there as the problems will always occur late at night, not at 10:00 AM on a Tuesday.