Hi, mquinn, and welcome!
I can tell you our experiences with these things. When it was time to insure our camper, I just called our insurance agent and explained what we'd done. I texted him a few pictures of the finished interior, including mechanicals, so he could see it was legit. He asked what dollar amount we wanted it insured for, and that's what he went with. He just added it to our existing auto policy, and now our trailer is fully covered for the amount we stated. I should add that our insurance agent is local, and we've had a longstanding relationship with him. That might have made it easier.
We have been to several KOAs with absolutely no problem. We really like KOA when we're not boondocking -- they're always nice, clean, well-run, and welcoming! I think they're really fun, safe places for kids. The only KOA that would not allow us in was in Las Vegas. Apparently there is a Las Vegas city ordinance that requires an RVIA sticker from the manufacturer to stay in any RV park within the city limits. When I spoke to the Las Vegas KOA manager, he said he'd love to have us but the local ordinance didn't allow it. Las Vegas is the only place we encountered any sort of problem.
At state park, state forest, and national park campgrounds, we have not had any problems. You might be surprised how many neighboring campers are curious to have a look inside and see what you've done.
Enjoy your build process, and take and post lots of pictures! I think you and your little girl will get years of enjoyment and lots of great memories out of this!
