I would try the RV dealer first to see if they have a key as was mentioned the CH 751 is very common. If not, do you have a locksmith close by if you do take a lock to them it should run you $15-20 to get one made. Then get several duplicates.
The storage compartment doors should normally be the same key. The main entrance door or doors have their own key.
Most do not realize the the tt storage compartment doors, are common keys. So are golf carts, & most small tractors of the same make.