Many states have gotten wise to the ol’ “it’s homebuilt” gag. MN is supposed to require submission of materials receipts, a shop receipt, or other evidence that you actually built the trailer or had it built by a shop. In some states, they want to see the actual trailer at the DMV.
There is always a way around the CMO issue. You just have to find the person at the DMV or the website that tells you what it is. It’s the same with missing titles, there’s a way to fix it, it just takes time and knowledge/research to know what to do.
Bottom line is I don’t specifically know what’s involved in CA, but be careful lying to the DMV about this. It doesn’t take them long to wise up to gags that can be used to register stolen trailers.