I would probably try cutting the template from cotton (a Docker’s weight of canvas) and then using a tacky spray to adhere the cotton to the VCP. Depending on how well the VCP cuts with an exacto knife (see jbv’s collection here) I’d consider adhering it to a big ol sheet of plywood/mdf to cut it out.
As for cutting out fabric larger than the glowforge bed, wrap the cloth around a dowel and IIRC there is a decent size gap to stuff it at the back of the crumb tray. Then just unroll it. Otherwise it looks like a custom crumb tray could be in your future. Presumably you have access to a Snapmark enabled glowforge.
So, are you going for functional use or more about style? If it’s style I just love the distressed look of a waxed/waterproofed canvas and leather accents - all glowforge-safe.