Hi there, just finished up my vent windows so I’m just a few steps ahead of you. Fortunately I had most my parts but I can tell you, tracking down the missing ones is a big PITA. There are actually a ton of parts and screws that go into these vent assemblies, I’d recommend getting the original assembly manual to guide you. The reprints are available from CJPP, but get the BODY assembly manual for the vents. I made the mistake thinking it would be in the interior assembly manual.
That is correct the assembly is sealed almost all the way around, I used 3M strip caulk to seal and there’s some pretty big gaps that need extra attention even with the assembly mounted correctly. You’ll want to make sure the channel is cleared out and openings for the drain hoses in good order, and be sure to use hose clips where they attach. I’d also recommend sealing the inside of the channel to prevent future rust issues.
I can snap a few pics of the completed install if you need, I haven’t installed the sail panels yet.