I've inspected the Roof of every RV we've owned yearly. Sometimes more often. A Self Leveling Silicone made for a Rubber roof is probably your best bet. I've always used White so I can see any separation. On the Side walls I actually remove as many of the doors, lights etc. and re-caulk them with an exterior sealing Putty, the same type product used when manufactured. Afterwards I use a pure White Silicone for a finished look. Again, the same way it's done when manufactured. This trailer is around for the long haul. Wax on, Wax off....