Your roof likely came with a warranty. To keep that warranty valid, you should inspect your roof regularly. You should be inspecting the sealants around everything on your roof and touching up or replacing the sealing material BEFORE a leak occurs. Depending on the type of roof material, your roof may also need cleaning and UV protection applied annually. The biggest cause of damage to an RV is a water leak! 

A common recommendation for towable campers is to inspect your brakes at least annually, and inspect and repack the wheel bearings every 12 months or 10,000 to 12,000 miles. I usually don't travel more than 10,000 miles a year so I inspect and repack my wheel bearings every Spring. While I have the wheel apart, I also inspect the brakes on my trailer. Brake repair should be done in a repair facility by brake experts. Wheel bearings can be inspected and repacked at your location. 

Depending on where you travel, your air conditioner can make all the difference between a wonderful trip and a sweaty disaster. Here in North Idaho I don't use my RV air conditioner much, but when I need it, I want it to work! When I travel south, it becomes just as important as my furnace when I am camping in the Spring, Summer, and Fall in the north. Your air conditioner should be inspected annually. 

Your propane furnace should also be cleaned and inspected annually. The burn chamber is a favorite location for visiting insects that can clog up the chamber and cause your furnace to stop working right when you need it the most. The constant heating and cooling will also cause metal fatigue leading to cracks in the burner assembly. There are several safety features of a modern propane furnace that will stop the furnace from working properly. 

Your hot water heater should also be cleaned and inspected annually. At the start of every season the water heater propane burner should be checked for any obstructions and cleaned. A water heater with a steel tank (Suburban) should have the anode checked and replaced if necessary.