It is amazing to read these threads. It is also very obvious that many people don't read anything about the situation before starting to fire from the hip. Several pages into the thread and people are still referring to the RV as a trailer which the OP clearly states is a Class C.
With all the lawyers in training and supposed real lawyers responding, it is interesting no-one has pointed out one very important fact. In every state, the sale of a motor vehicle is not considered to have been consummated until such time the title is transferred to a new owner. The fact that the previous owner signs the title and gives it to the new owner does not consummate the deal until such time the vehicle is actually titled in the new owners name.
This is a point of law that most dealers are aware of for they deal with it almost daily. The time period between the sale of a vehicle and when it is actually titled to the new owner does hold a legal liability to the dealer in case of an accident. Until the title is transferred, the dealer is the legal owner of the vehicle and as such can be added to any lawsuit arising from an event during this time. A dealer's Garage Keepers Liability Policy should always have coverage for this eventuality if the dealer is paying attention.
In this particular case, it could be argued that both the buyer and seller are best covered by driving the vehicle in transit with the seller's tags. Until such time that the title is changed to the buyer's name by a DMV, the seller is the legal owner. This can be argued regardless of whether the two parties have signed the title or not and executed a bill of sale. Any seller would be well served to not cancel insurance coverage on a sold vehicle until such time they are confident the title has actually been transferred. In case of an accident, the seller would then have some protection in a case where the damaged party would choose to argue a legal transfer of ownership had not actually taken place.