Because of gravity, it would be difficult to use it horizontally...the pleats are designed for vertical installation...
If you are referring to the Redi Shade Cut to size temporary shade. You can screw them in but it is not necessary, each paper shade comes with a strip or glue already on it. All you have to do is cut to your size needed and peel and stick. They come in two sizes 36x72 and 48x72.
The top. It fastens by the tape strip.
They are sold in a single (1) pack and maybe a double (2) pack.
Depth is 1.25 inches
Yes, I have purchased white previously.
Those shades are 36'' wide so if you are looking for something of 56'' wide, it will be too small. You could potentially buy two and cut them appropriately to be side by side but I am not sure how good it would look.
I would say it will be warmer than white and cooler than nothing.