I have read several threads regarding construction of modular/relocatable layouts. Occasionally, someone recommends fastening plywood sub-roadbed sheets to box frames using cleats under the sheet so that the top may be unfastened from below and/or so screw heads do not conflict with track and scenery construction as they might if driven from the top. Has anyone attempted to secure the sheet (whether plywood or foam) to the box frame with Velcro (assuming that the box frame is sufficiently rigid without the top sheet)?
I’ve never tried Velcro, and don’t know anybody who has. The issue I would see with the Velcro method is that both the top sheet and the box frame have to sufficient structural rigidity on their own, instead of complimenting each other as screwed (or even better, glued) construction does. Your suggested method depends on gravity for vertical fastening (with limited help from Velcro) and the Velcro for horizontal. I don’t believe either will do a good job in stabilizing a plywood sheet against warping or moisture content-driven changes.
You might succeed with a foam sheet, simply because there aren’t the forces such as moisture content to deal with. However, in most cases the box frame not only supports the foam sheet, but also protects the compressible edges. You would lose the protection benefit, as well as the support against the sheet sagging and bending if you separated the 2 pieces for moving. The sagging and bending when separated from the frame issue applies to plywood, too.
I guess I’m trying to see the advantage of your Velcro proposal instead of unifying the top sheet and box frame.
my thoughts, your choices
Fred W
Thanks, Fred – you make sense! Dante
Format follow-up (or is it “foul-up”?): Don’t know why the quote looks the way it does; it was quite normal in the preview! 
This might be a good project for a Pocket Hole jig. Inside the box frame, up from the bottom, you would get structural strength with no visible screws.
The screws would still be there though, if you accidently drilled into that area, so you’d have to stay aware of them, but you won’t see them from the top.