Hi Tom,
Nice little units - and love the small print, made me chuckle. Some people eh?

Personally I would use plywood, just because I don't like MDF dust, but the concept is sound. My first machine did use 4 spacer tubes as Ross suggested, but if you have limited hand tools it can be tricky to cut 4 tubes exactly the same length. There are ways of course, but the spacers guarantee a pretty square mounting surface.

George,
Think, then type, not the other way around .