Errr… if you have a burning desire to not own stuff and live in a small space, why not just rent a small apartment? Landlords are no fun to deal with, but homeownership has it’s own special challenges. Buying a tiny, hard-to-sell, place seems to be the opposite of “not owning stuff”.
And an unsecured loan is, by definition, not a “tiny house” loan (or wedding loan, or divorce, or adoption, or whatever loan), it’s just a line of credit. There’s no need to go to a special lender for this; any bank or credit union can quote you such a loan if you qualify.
And the interest rate is “likely” to be higher? In a world where you can buy a house for 4%, and a car for 2%, it’s 100% guaranteed that any unsecured loan will be higher.
Seems to me that it would make the most sense to just buy a used single-wide (if you want to stay put) or a used RV (if you don’t) and call it a day.