My windows are not frameless, but I believe that the frameless windows are put in the same way as my framed windows - a ring on the inside, screws go from the inside ring to the outside window structure and are tightened to squeeze the two halves of the window together. There is a foam strip between the side of the trailer and the window structure which makes a seal. That foam strip does not make for a lifetime install and can leak.
A cap seal is a bead of caulk applied at the place where the structure of the window meets the side of the trailer, all across the top and down the sides at least past the curve. The caulking helps insure against leaks. For more leak protection, many have removed the windows and replaced the factory foam seal with butyl and applied a cap seal . Windows are a common source of leakage, and at least the caulk cap is a good idea.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch