I just inspect my roof twice a year and apply Dicor self leveling lap sealant to any areas that look like they may need some refreshing. This would be around the vents, the front cap seal, tv antenna, skylight, etc. To be honest, in the 5 years I have owned the trailer I have not had to use much as the original caulking still looks good in most areas. Its about time for me to go up and inspect again though.
2004 Chevy 2500HD Crew Cab 6.0l, 4.10r
2010 Jayco Jayflight 28BHS
Reese Strait Line with Dual Cam
P3 Brk controller