I went with 3/16 UHMW.
The plastic has backer throughout whether it the 2x2 floor joists of foam board so 3/16 is plenty thick.
If it were hollow on the back side I would probably go thicker.
I have 2 spear holes which have 2 round hole covers in each spear door.
I once pull the house right after a good powder snow. I did get some snow blow up around door/cover seams in the floor.
Otherwise snow fills the spear hole cavity creating a seal and I get very little in the house.
I did not have the interior finished last winter.
Any exposed aluminum will build up frost and then drip.
I'm in the process of adding ferring strips and 1/2 foam board to the interior to cover any aluminum and cedar T&G interior.
I'm concerned if I don't have the interior sealed tight warm humid air can get to the aluminum, condense and create a wet spot.
I think if I was to do it again I would ferr and add foam board to the exterior keeping the aluminum from freezing.
1' x 2' Anderson window
I use it as a spear house so I didn't want a lot of window to cover, just something to peak out of
Not a problem, it's been a fun build.
Look forward to using it again this winter