Are you buying from a private party or from the resort developer. If the latter I'd think they'd have potential lenders they can point you towards. I agree, lenders will typically require a larger down payment on what they consider "empty land".
There are other options too. Do you own your home? Paid off or lots of equity? Refinance and take the full cost of the RV lot out (paying cash for the lot). This is what we did knowing we'd be selling the house in a year or so, a home refinance is easy to get these days - but this only works if you have enough equity. When we did sell the house we walked away with no mortgage, a fully paid for RV lot.
Jay & Peggy Monroe with Dolly
Can't take it with you - don't plan on leaving any behind
2016 Newmar London Aire 4553, Spartan chassis
Wrangler Unlimited toad