You really only need one layer of glass if you're going over external grade ply. But if you're not just wanting to practice your glass skills, consider these options:

- the good old 'PVC pipe'. Durable, relatively cheap if you know how to look for it. There has been a hurricane or two, and there well might be stuff lying about.

- Connected with a fabrication shop? Have a box made if you can get next to a metal brake... actually, if you have a friend who would also like a box, by the time you buy the material for one, it's prolly about the same price to do two and you can share the cost.

- Consider finding a used back-of-truck tool box and refabbing it to your needs. Dividers can be easily cut out with an angle grinder.