I'm a dealer and have customers run into this occasionally.
If you can, try to get insurance online through one of the big online companies.
I would avoid ever saying the words "conversion, RV, commercial, delivery vehicle", or anything of the sort.
If you are going to use it as a commercial vehicle, by all means get the appropriate insurance, but if this is a personal vehicle, it is just that, a personal vehicle.
It can be done, I've seen people get it done easy, and I've seen it take a week to get squared away.
Personally, I'd avoid explaining anything beyond the fact that this is basic Promaster is what I choose to drive, and it is not a commercial vehicle.... who knows, maybe you like to surf, and need the space for boards....