Suggestions for clear panel at bottom of skylight well

I have a skylight with a large well, about a 3 X 5 ft. opening at the ceiling. I’d like to put in place some kind of clear panel at the bottom (ceiling surface) in order to reduce heat loss in the winter. I’m not seeking a tight seal, but rather something to stop bulk air movement up into the well.
Tempered glass panels would be nice, but too expensive for me. I’ve been considering just using the clear acrylic panels that are made for larger ceiling light fixtures, but my impression is that such material is quite flexible and would sag. I had the thought to make frames for several narrower panels of such material, say 1.3 ft. X 3 ft, and use them to cover the opening, but that seems like a hassle. I also that that perhaps just gluing strips of wood (say 1/4″ X 1-1/2″ X 3 ft.) on the edges of the backs of the acrylic panels would stiffen them up.
So, I’m seeking ideas or suggestions to accomplish this. Perhaps someone has thought of a completely different kind of approach?
Replies
You can buy cut-to-order acrylic panels at many "full service" hardware stores (and, of course, at glass supply places). 1/4" of the stuff is fairly stiff, though I don't know if you can get something as large as 3x5.
But note that blocking the bottom of the well will encourage condensation. You need to have some ventillation in there or otherwise keep it dry.
I made some inside storm window type panels for a friend's skylights. I made wood frames for these. I cut a groove into the perimeter of the frame into which the plexi glass fit....this helps with sagging. I attached adhesive faced foam weather stripping to the frame edge to air seal to the window frame. Attached to the window frame with screws. Really cut down the cold draft.