First, check local codes/zoning and make sure you can live in an RV at the warehouse. Sooner or later a concerned or nosey neighbor may call the authorities.
Out west, there are many places to boon dock at little to no cost. Browse some full-time RVer's blogs for more research.
I have read some blog posts from retirees who are succeeding at what you propose. However, I suspect that those who end up broke and stranded some where don't have the where withal to post those stories.
I would have an exit plan that includes emergency repairs or travel to a home base.
Also, I'm not too sure about your financing plan. Banks are most likely very reluctant to finance an RV as old as you will have to find to meet your price point. I haven't shopped for old MHs or tried to finance one, either. Maybe you have an alternate financing plan?
You may be better served to find a really, really old MH for cheap. Shop around. They are out there. Many have sat for extended periods of time. Take your time and make sure it is mechanically sound.
With a year or two to bring it up to shape, you could make quite a few repairs to the house in that time using out of pocket money. Then, you could avoid financing. If you find a mechanically sound RV with a sound roof that needs a new AC, furnace and some other house stuff, you can work on that or find a mobile RV tech to do the tough jobs. Many RVs are orphaned when a spouse loses his/her health or dies, and they sit. Sooner or later, someone just wants to get rid of it.
Some of the systems may need costly repairs or just simple things. This is why someone already asked you how mechanically savvy you are. If not, you will use the check book for repairs. That can get costly.
Good luck to you.