I’m looking to make a rough and ready layout for the kids which is naturally a stepping stone into better things to come - whether that’s for them or me

space is as ever at a premium but I’m thinking of storing it under a king size bed when not in use (not a divan - so there’s plenty of height)
6’ x 4’ would fit the bill as it fits nicely under the bed and allows for continuous running. there’s some fab track plans for this beginner size in another thread in this forum. Yes I’m aware this shape/size is far from ideal, but I have to balance this with being a family home!
As the kids will move this, it needs to be light but strong. I took inspiration for a Celotex/kingspan insulation board base from this:
https://www.youtube.com/watch?v=E_8WzxHrhlI
Anyway onto my questions:
1) I don’t think Celotex (25 or 50mm) will be rigid enough for frequent movement, so Im thinking it needs mounting onto a thin (4mm?) ply base, and with a rigid frame. seems a lot quicker and easier than a conventional board on a frame. Any comments?
2) I’m looking for ideas to allow quick and easy addition/removal of legs to get it off the floor. Conventional screw mounted legs wouldn’t work well with the celotex/thin ply construction and certainly would be a pain to assemble/remove frequently. Anyone used trestles? Something like this
https://www.screwfix.com/p/sawhorse-10-2cm-2-pack/7965p
could I get away with 2 or would that be quite unstable on a 6x4 board and need 4?
Appreciate any feedback