I'm going to use these as the base for an ironing surface-my plan is to get a 3/4" plywood top that is about 3" bigger all around. I'm not sure if I'll use all 5 across or just 4. I'm thinking 4 would be plenty. So anyway, I need it about 6" higher and while I was doing something near them today, it occurred to me that it would be a pain if I dropped something in behind them (since they'll need to be away from the wall so I can let fabric drape on both sides of the surface plus the topper overhang) and maybe it would be good to put them on a solid board with casters attached, which might add enough height (doesn't have to be exactly 6"). Has anyone done this?