For the bed seals on our old 2003 Kiwi 17a I used Turtle Wax F-21 twice a year. When we traded the trailer after 10 years the seals were still soft and had no leaks. I'm going to continue using it for our X20E.
The slide out is new for us. The main thing I was told was not to use anything petroleum based that will will attract dust and dirt. I think we're going to try the baby powder.
2013 Jayco Jayfeather X20 E, 2008 GMC Sierra 1500 Crew Cab Z71 SLE