The RV manufacturer set the MSRP with the assumption that it included any necessary dealer prep but not any delivery/shipping costs from factory to dealer. That cost varies widely with the distance, timeliness, and method of delivery. Automobiles, trucks, and heavy equipment are all priced the same way.
When RV dealers began to steeply discount (25% or more) their advertised price, it became common to exclude prep and perhaps other necessary services from the selling price and add it back in as a fee, thus enabling them to advertise a more attractive price. Naive buyers who fail to get a bottom-line (out-the-door) price quote often get surprised with the add-ons. Other items often added back as a fee include documentation fee (filling out the required paperwork), dealer fee (extra profit), and pre-delivery inspection.