Deposites are RARELY refundable (they serve no purpose if they are). If you were mislead in WRITING then you may have a case of the breach of contract is substantial but if it's a minor issue like a slightly larger or smaller tank size (for example) or similar minor items, probably never get the deposit returned. If it's major breach like It's a duel axle and has only one (AND IN WRITING) or if weighs a maximum of 5,000 lb. and it's 10,000 then should be no problem to get deposit returned.
WITHOUT a deposit it is unlikely that ANY dealer will special order an RV for you but you can always purchase one off of his lot with no deposit. If the RV is in his inventory then the only reason for a deposit is to hold the RV until you can arrange for a loan or come in to sign paper work.
Good luck / Skip