From just googling, it seems building an enclosure, rack, cabinets, etc. with plywood has quite a few cons to it. Some people used it, but there is a reason why it's not popular. PVC overall is very reliable, very light (almost like foam), and won't crack or break under screws. Personally, I would go with the tried and true methods and materials, especially with an enclosure you want to make so complex, I would assume you want it to last awhile without risk of cracking or warping.