https://www.amazon.com/dp/B0009YIE1O...v_ov_lig_dp_it
This is your competition price wise. Yours is better, but people aren't buying even these.
If someone didn't buy this(I still haven't), they won't buy yours. I'd buy yours, the model comparable to yours is $425 but I like to make life as comfortable as possible so I'd go for the expensive unit. Almost all rv owners haven't even gone for the $75ish(the price these are almost always available in Amazon warehouse) model, and they'll not convince.
The liability of selling one you've built yourself is mind boggling.
Take a look at the
'my golf cart has rights' thread
and modify it so he has backed into something and damaged a vehicle with your home built tire rack or put 1750lbs of some sort of footpounds inducing extension.
Punchline:
If you've the stomach for it all, I'm possibly in for $300 shipped just so I don't have to modify that linked unit.
I don't know what someone without the wherewithal to customize, not the want to spend the $75+- for the linked unit would do.
Personal inabilities and lack of roadside assistance are the need for the fold down part of the mount unless there is a rear compartment that needs access. I think very few rv's have an insurrmountable rear access problem.
Your market is limited to those with an access problem and those who can't lift a wheel from the mount but think they can change a flat themselves. Other than those folks, the linked unit would work just fine.