I have a Domestic 2804 frig in my RV, The freezer works great but the frig part will not cool at all, can you help

All cooling takes place in the freezer. The refrig/fresh food side is a parasite, depending on cold air circulation from the freezer side. The fan in the freezer provides that circulation, and usually the freezer control setting determines how much air is moved into the refrig side.
If the fan is up to speed and the both controls are set in a middle position, the refrig side should be fine. if the problem continues, replace evaporator fan motor or clear the blockage preventing circulation (usually frost build-up from a defective defrost system part or blocked defrost drain).