Welcome!
There are two options for what you're doing- RV putty tape or butyl tape:
Putty Tape: This is what Sunline originally built the trailer with. It's usually sold in about a 25' or 50' roll at an RV dealer. Putty tape is easier to work with than Butyl because it isn't so sticky. It doesn't have a terribly long shelf life because it dries out and hardens a bit where it would be hard to work with. It does the job but over time, parts of it can dry out and separate from either the trailer wall or the window/door, which can cause water to enter. This roll is usually a couple dollars cheaper that butyl as well.
Butyl Tape: Butyl is more flexible, seems to have a longer shelf life, and is much stickier to work with. Like it's hard to get the piece off your hands in tact, so don't press too hard lol. But this stickiness is good, because it sticks to the surface and helps to retain the seal long term. It's considered a bit of an upgrade over putty tape and has a very slight price premium for the roll.
In my opinion, if you have the part off and are going through the trouble to redo the seal, go with the butyl.
Whichever you use, I recommend cleaning the surfaces on both sides before reinstalling, especially if there's any dirt visible.
The tops of the front and rear clearance lights and the roof seals use a slightly different sealer. The roof components use the same tape described above, but there's an extra step to coat all those seams with the other sealer, which depends on the type of roof that you have (aluminum or rubber). If you haven't sealed the roof, you should consider doing it soon.
