The gasket referred to is for the solid non opening window that the 1971 and earlier Trilliums had. Much like the Bolers. Your trailer has all jalousie windows
, except for the door. The repair for those goes like this:
1) remove the black covers over the screws. They will likely break due to age. They can be replaced:
2) Remove the screws. Don't worry, the windows won't fall
3) Pry out the windows. Work your way around the window with a pry bar, or large putty knife, or whatever, (I used an ice chopper). You should have help for this. Someone to make sure you don't drop the window
4) If you have shelves above the window, this is the time to remove them. The shelves are attached to the wood that holds the windows in. I did not compleatly remove the aluminum and wood shelves in my 4500. I just unscrewed them from the frame, and pushed them up.
5) This is the hard part. Separate the Ensolite from the plywood frames. This will take patience and luck. Go slow. I used a boxing knife, others have used a putty knife. Try not to go through the white layer.
6) Clean fibreglass of all old putty residue.
7) Make new frames. I would suggest 3/4" marine plywood. Maybe even paint
it. Some use other materials that are less likely to rot. I figure, if regular plywood lasted over 20 years, then marine plywood should do at least as well.
8) Put the frame back in. I did not use glue, or anything here. The Ensolite was enough to hold it in place.
9) Put butyl tape on the fibreglass where the window flange will cover it.
10) Screw the window back in. I started in the middle of the flange and worked my way to to corners. I am not sure there is a preferred way to do this.
11) Trim the excess butyl tape that will have squeezed out. Use a soft plastic, or wood implement for this so you don't scratch the fibreglass.
12) Install the screw covers.