We own a small one. Bought an existing park just over three years ago after looking into developing a park. Before you get too far along, check with the county/city permitting folks and get a copy of their ordinance or rules regulating RV parks. Of course these things vary with the location, but some can almost kill a deal (hopefully before you get started).
When I checked into developing a park, I found I had to have a drainage study done and it would involve a retention pond. The size would depend on the drainage study. In some areas, it isn't a big deal, in others you can wind up using up a decent size chunk of your real estate. The study was quite expensive.
A lot of parks in our area have rock roads but the rules changed a few years ago and that is no longer allowed. Have to go with concrete, asphalt, or chip seal under the new rules. Adds greatly to the cost.
Another thing to consider is what utilities are available at your two tracts. I would never build a park where I had to have my own water well. Ours has municipal water and sewer. While not having sewer and having to use a septic system would not cause me to back off, having to have a water well would. Even with municipal water and sewer, we were going to have to put in a lift station, back then they quoted us $23,000 on that.
Another thing about developing your own park is having to make a guess at what sort of occupancy you might expect to see what sort of return you can get on your investment. If buying an existing park, you have some idea about what has happened in the past. There are different types of RV parks and two common ones are destination parks (where people want to be in that location because of something in that area, such as the beach, a lake, etc.) and those geared to long-term workers. Ours is the latter.
I will tell you that the cost of building one is likely going to be higher than you think, at least it was for me. And even though we own stock in the bank we do business with (it is a locally owned bank, not publicly traded), they would not lend on an RV park and consider any income from the park in determining if they would make a loan. In other words, qualifying for the loan would be based on other income and assuming the RV park netted to zero.
A couple of things to consider. Be sure each site has 30 and 50 amp hookups, don't build so that some have 30 and some have 50. Have both on each pedestal. A lot of folks ask for pull through sites. We don't have any, all of ours are back in, but our road through the park is like 50 feet wide so that backing into a space is not difficult like if the road was rather narrow. I would suggest having some pull-through sites. To maximize the number of spaces per acre will mean you still will need some back in sites. I suggest having them at an angle (45 degrees or something) to your roads rather than perpendicular (90 degrees), makes for easier back in for your tenants.
And while density is important (sites per acre), I suggest building larger sites, 30 by 70 or so or even 35 by 80. The bigger units with multiple slide outs require more room. Having bigger sites will get you a better class of tenants over time. Our park has nothing behind the two rows of sites, so many of our folks park their bass boats, or bay boats, behind their RV. Almost all of the other parks do not have that kind of room. In fact, we got two guys this week who chose our park because there was room for their bass boats.
The electrical is going to blow your mind. We bought our park as I mentioned and are completing building a new office, laundry, shower, rec room and ran wire to it and used copper rather than aluminum and it was expensive.
A suggestion on your water lines, do a loop feed and put a cut off between each space. That will mean having an inexpensive 3/4" valve between each space. But if someone breaks the water line, you can shut off the valves on either side and only that space will be without water.
Having said all that, RV parks (provided you are in the right location) are pretty good cash cows. I have really enjoyed ours. I am a CPA and have detest that sort of work in recent years but love going to the park. I like to go mow, visit with the folks, and look forward to going down there. My son runs the place (and soon will own it) and I cover for him on some days. We treat people like we would want to be treated, and not many seem to do that. As such, we get a lot of repeat business and referrals.
If you have any questions let me know and I will be happy to try to answer them.