I've been using silicon spray since I got my first Jayco with a slideout in 1998. Works great. Put the little extension applicator in it and spray away. Don't let anyone tell you otherwise.
2014 Jayco Jay Flight 33RLDS travel trailer, 2005 Chevy 2500 Duramax diesel with 60 gallon auxilary bed mounted fuel tank, Honda EU3000 generator.