How can I attach casters to a 1/4" plywood board when I only have access to one side? I built a prop that consists of a box with casters on the bottom. The bottom of the box is 1/4" plywood. The casters are attached with machine screws; the nut and top of the screw are hidden by fabric sewn to the inside of the box. The fabric does not have any way for me to remove it for easy access to the plywood board on the bottom of the box; it's sewn in.

One of the casters got tired of the abuse I put it to, and broke off. (The plate that attaches to the box is still fine, but I'm going to have to remove it.)

   |X|     nut
}}}}X{{{{  wood
   _X____  caster plate
   XXX     head of screw


How can I attach new casters to the bottom of this box without ripping out the fabric on the inside? I have some Molly bolts, but they're not good for attaching to 1/4" thick boards.

For reference, the box looks like this. You can just see one of the casters peeking out from under the missing legs on the left.



Can a replace these casters without having access to the inside of the box?

Usage: I drag this thing around city streets and buildings. It's following me via fishing line, which means that for most bumps, curbs, sidewalk seams, and doorjambs, I'm just walking forward and assuming the box will keep up.
A butterfly anchor (also called a toggle bolt) allows you to drill into the plywood and insert the toggle from the accessible side. Then tighten and the bolt will hold very tight. Enjoy!