I secured my insulating pad in this manner:
1. Bought 1" X 1/4" fur strips (HD, Lowes, etc.).
2. Drilled 3/16" holes thru them every foot or so ("eyeball" is close enough and, in my case, I drilled holes 2" from each end, 1 in the middle between the end holes and 2 more splitting the difference between the middle and end screws).
3. Bought a pound of 1" long drywall screws and some fender washers.
4. Screwed the strips to the underside of the mattress platform to form an outline 'frame' that clears the walls of the bed riser when the bed is closed.
5. Fastened 6 additional width-wise strips just long enough to clear the inside width of the 'frame' strips.
When fastening the strips, run the screws in just far enough to fasten the strips so they avoid having their points come through the bed's platform or split the fur strips.
You'll never have to worry about that again.
Bob (Squidly Down Under) & Peg - 2013 Ford Focus pushing a 2011 Phoenix Cruiser 2552S
"In God we trust" to preserve our country and bring our Troops safely home.
Carry on, regardless..................