I do not know all the in's and out's of this and each state has different rules.
In some cases people make their own trailers out of various commercial bought parts and normal wood and steel components. In this case there is no manufacture of the trailer.
When the trailer is registered they put in "home made" as the manufacture. The trailer still has to comply with all regulations for lighting and safety and it might need an inspection.
Before going this route, check out all the things that may come along with that decision. If the camper is of great value, then a home made trailer may need to get appraised to have RV insurance on it for theft and fire. If you are going with an auto policy adder for a trailer which is depreciated value payout, that may or may not be a good deal all depending on the actual value you want to recoup in the event of a total loss. Point being talk to your insurance agent before going the home made route.
Also check out what a salvage title means once the trailer is declared that way. Does it mean that the trailer has to be inspected before it can be used on the road? Do not know what that all entails on the inspection or who does it but I have heard this needs to happen in some cases.
Here is a fast hit on the web on this. This seems to be for the state of Georgia
https://dor.georgia.gov/titles-rebuilt-or-restored-vehicles
See if the state in which your friend lives in maybe has a web page from their state.
Here is another hit on the web. Do not know the validity of it but it brings up some good questions.
https://www.thebalance.com/how-to-get-a-salvage-title-removed-on-a-vehicle-527543
Please let us know how this turns out. It is a good topic to know how at least someone came out with it and in what state they did it in.
Hope this helps
John