Inspect it regularly and get to know what it looks like so you'll notice changes. Be proactive regarding renewing sealant or consider taping all the seams. If you want to clean it bucket and brush with mild dish soap. Void power sprayers and strong cleaners.
Annual smoke testing might be a bit more then your RV budget can afford but the test results will disclose any leaks not only in the roof but everywhere in particular the sidewalls around the windows and such. If the coach is new to you I would consider it.