OK the cloth arrived - turns out it's completely black rather than the 'salt 'n' pepper' style as per the listing. (although looking at the photo of my amp it kind of depends on the lighting)
For now I've covered the grille of the amp, which works fine as the curved ends of the grille actually do a great job of grabbing the cloth and holding it. I'll still make a wooden frame though next week. Here's a quick snap. Really pleased with how it looks now, nice and clean!
I might get a folding handle for the top, like a flight case style sprung handle.
Any ideas what I can call it, there's room for a logo on the top front edge (with a label gun!!)