Looking at the restrictions for bank mortgages on premanufactured trailer homes, I am not surprised that potential owners of converted shipping crates have difficulty securing a mortgage.
Perhaps dropping one of these units in a trailer park would give you a legal place to reside and therefore get funding, but if you are going to do that, why not just buy a traditional trailer? And if you are going to put one of these on a cottage lot, why not just build a small cottage on a foundation with its traditional mortgage, and its more guaranteed resale potential?
I honestly don't see the point of this business model, and if it isn't succeeding, maybe rethinking it is the best thing. Just because you can do it, doesn't guarantee buyers want it.