Whilst building a prototype layout for WTC I used perspex but both glues (superglue & gorilla glue) I tried failed to bond, so I'm thinking of using GRP sheet to build the inner frames and the end caps using an epoxy glue.
2 x 5mm disks could form the inner part of the end caps with room for 2 O-rings and a 3rd oversize as the outer. I can turn the disks on a lath to get the close fit.
I am intending to use 75mm polycrbonate tube for the outer tube, as polycarbonate seem to be prefered over acrylic.
The only down side I can think of is that I have heard GRP can absorb water and because of the fibres the surface mght not be as smooth as resin, perspex or similar materials.