Gail, thank you for replying. We did end up using a two part epoxy to glue the track and guide down. My son has clamps and was able to clamp the track down pretty good. The problem was, he misread the instructions and switched the tubes of epoxy. So, instead of using 1 part to 2 parts. He used 2 parts to 1 part. The adhesion was fast and strong and he said that if he had done it right, there might have been enough time to align the track with his marks. It's off a fraction; so, I suggested he measure in for the guide to match where the track ended up.
We went to Ace yesterday to get some plexiglass. But, their cutter is broken; so, I don't know if it broke while it was cutting our pieces or what. We got 1/8 inch thick; because, that is the size of the track and guide that I got. Ace didn't have enough acrylic to cut both doors; but, did have enough to cut one door and the sheet for my son's palette. The 1/8 inch acrylic will work for now. At some point, I will probably get some tempered glass. My son used this thickness in his last palette and said it did not flex, even when he was using a 4 inch brush to pick up his oil paint. He said he gets kind of wild when he's packing the paint into the brush.