I've done some construction with black foam core board, available at art
supply stores. It makes a very rigid box when glued. Can be cut at
weird angles to fit a open notebook computer. Joints can be reinforced
with linen tape (also art store). Surface made water resistant with a
varnish/paint or painting media (e.g., acrylic gel media). No reason to
have the view port larger than 2.5" x 6", plus a slot to allow
finger/hand access to keys. Include a bottom on which the computer sets
so that it cannot easily be knocked over. Black cloth to cover ports
around hands and when not being accessed.
I'll show you my foam core cover at Shingletown (Yippee!!!)
Robert