I'm trying to understand if I can legally advertise these spots (3), perhaps put more, as long-term RV slots.

but I will take a guess at what your askingif the developer is going to bust this into lots and you stay in you just lost your tax advantages and will be deemed a dealer at the highest tax rates.sell now no risk.. and best tax treatment you could 1031.if its one property and your saying should I partner and they are going to build an apartment on it and we will keep it.. that's different.. but you lose control because your now going to put a massive amount of debt on it.. all though in your area not too risky given market conditions.. and really depends on your developer  known, reputable and stable ?

Form a legal partnership with all the outlines for who gets what, who contributes what. 

My contractor knows he needs to pull permits, but I want to be safe work a legally binding agreement/document.

Make sure you have the before and after pictures for legal purposes If it comes to that.

Do not rely on it for legal advice.

I believe tax debt has to be below 50k to get approved for a loan.

What would be the legal course of action?

Many years ago after I had two different agents snake deals out from under me I took the class to see if what they did was legal.

The bad egg has a 505 credit score with almost $130K in debt between student loans, car, and credit card debt.