How to get a loan for RV

Ex-banker here. You are not going to get a loan at any conventional bank or financial institution. Your credit scores are too low and your credit history too limited, you have no residential stability and are looking at purchasing an item with very limited collateral value. If you are capable of making a large down payment, a dealership might have a lender that would make an exception. If you have very strong employment stability, maybe, just maybe, a credit union affiliated with your line of work would take a chance. While your story is sad and sadly familiar to many, it makes you a very poor credit risk. Lenders have no way of knowing, and you have no way of proving, that your ten years of bad luck and problems has or will end.
My suggestion is make an application at a couple of dealerships and see for yourself what is going to happen. The dealership has every incentive to get you approved. If they can't make it happen, and you don't have an inside track at a credit union or a relative who is a bank executive you will need to pivot to another plan, and that is not the end of the world.
One other note. You say you are a high income earner with no debt, if that is the case why couldn't you buckle down and save up enough for an inexpensive rV in a matter of a few months.

I understand the points you are making. My income fluctuates between 120-140K based on the project which is not at all unusual in the DC area. I could put away 2-3K/month meaning in a year I should have something accumulated for a purchase but it's long and painful. The problem with that route, I have to live somewhere during that time and apartments and all housing, whether buying or renting is insanely expensive, a decent apartment is close to 2 grand. Which makes saving that much harder.

An RV purchase under unfavorable terms with a high interest rate is a lot better than blowing 20K/year on rent. I spent 100K on rent in the last 5 years. About 150K in rent in the last 10 years. This makes no sense whatsoever. I could not buy a house because at the time my ex had full custody and I feared that she would relocate far away, to another part of the state or even another state, meaning I would have gotten stuck with a useless house. In retrospect, I should have brought something 10 or 20 years ago, but oh well.

Doing it yourself without a bank is long and painful. I could be happy with something like an old heavy-duty Suburban puling an old 30' TT. It's not exactly what I want but 80% of what I want. But both combined would cost at least 20K, maybe 30K so it's a year or two of painful saving. Hard to save money in in the DC area even with high income.

I think everyone successful here lives on dual incomes. One goes towards real estate, another towards everything else. 100K doesn't mean beans here.

I have a Tahoe now with the 5.3L, I realize it is a very limited TV but maybe I could get something uber-compact and light, a 19' TT I can pull. And make it do for a year or two. I should upgrade the Tahoe to a Suburban, ideally heavy duty with the 6.0L engine but they are so much more expensive than the base version.