I think it could be done, and it could work out very well. On the other hand it could turn out to be a nightmare. Lot's of downside risk as I see it.
60K or 120K is not chump change. It is not like you are splitting buying a 1000 dollar utility trailer. That kind of money (120K) can really screw ones life up. If the deal goes south.
I would want a contract that spelled out every detail, drawn up by an attorney, and legally enforceable. Problem is though, how would you collect if they go BK, or hide their money? Almost impossible
I would want to know the person's credit history and a financial statement.
My big worry aside from the above, would be what happens if one partner wants out? What if he got sick? or died? or was going to move across country? People's life change.
How will that be handled? Unless you have the horses to buy him out, that would be a big red flag.
Trying to get someone to buy half a 120K motorhome, would be I think very difficult.
As for buying on your own for 60K v 120K with a partner. I would say better a hovel in heaven than a mansion in hell. In my opinion just not worth the severe stress and sleepless nights that could happen. Way to much downside risk I think.