Can't speak for all states, but in Montana and every other state I have lived in, the dealer does not file any paperwork when they buy or take a vehicle in trade. They get the title from the previous owner (or the lien holder if the state is one where they finance company holds the title until the debt is cleared) and they complete the paperwork and send that title with proper assignment and the appropriate paperwork to the state and a new title in the name of the new owner is issued.
The problem here is the OP bought out of state. The dealer in this situation just completes the assignment information on the old title and gives or sends it to buyer. It is the buyer's responsibility to register and complete the transfer (often involving paying sales tax) in their state. The dealer's state DMV will have no record of the transfer.
It is also common for the dealer to not have the title available at the time of sale. They may have traded for the vehicle that had a lien and are waiting for that financial institution to forward them the title. The title might be held by the dealer offsite. The title might be held by the dealer's bank as collateral and isn't released until the dealer makes a payment. In all those instances the title would be sent to the customer after the sale.
It's been FOUR years and just now is the customer looking for the title. The dealer likely will claim (rightly or wrongly) they sent it to them 4 years ago. They may not want to get involved with chasing down a title on a transaction they completed years ago. Depending on the laws in the state, they may not even be required to keep documentation that they could use to prove whether or not they sent the title (certified mail receipt etc) after 4 years.
Put yourself in the dealer's shoes. How much effort would you put into finding something for someone who bought something from you 4 years ago and they are just now saying they never got it? What if getting a replacement title means the dealer has to call someone they bought it from 4 years ago and start explaining why they need them to apply for a new title? Wouldn't you as the person who traded in that RV four years ago think something unsavory was in the works? It is likely this is a can of worms the dealer has no interest in opening.
