I know you posted you were looking for other options, but the rubber bands really are easy to use, and easy to attach/detach with a homemade board.
If you look here, you'll see a homemade roll board I made.
http://festoolownersgroup.com/festool-jigs-tool-enhancements/home-made-sysports/msg103724/#msg103724
Pictures 5 & 6
It's hard to see but what I did was trace out the Systainer footprint, and specifically mark the area where the nubs stick out.
I routed a slight recess on the plywood base (about 3/16" deep) to lower the rubber band’s attachment point (you do need a slight amount of tension).
Then I drilled four small holes (1/8”) through the board in each recess. Two holes very close to eachother, and the pair spaced about 1” apart from the other pair.
I’ve attached a very rough picture showing this. The green dots are the holes I drilled.
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I then used some small zip ties to secure the rubber retainer clips to the plywood, by threading it through the two holes that form a pair.
Since the rubber bands only have to support the weight of the roll board, there isn't much strain or need for a super-robust connection. So the zip ties were totally sufficient.
I used this board for about a year, but didn’t move it around all that much. I made it specifically to fit in that cubby.
Unfortunately, I can’t post more detailed and up close pictures as I wound up purchasing two of the Tanos Systainer “caster cart” (on sale, natch!) and disassembled my homemade roll board.
The rubber bands are $3.00. So it’s a very cheap experiment if you decide to try it. The caster wheels you use are the biggest cost. I had it on HF 360o steel casters… I won’t do that again (they clogged with sawdust).
http://www.systainerworld.com/Tanos_Mobile_Accessories_s/50.htm
Now, an alternative:
One thought I had involved the use of a hinged/pivoting “T hook”. I never find quite the right hardware to use. But here’s an example:
http://teamathleticgroup.com/product/1-swivel-t-hook-tfa110/
Basically, attach it somehow. Then flip it up to secure the Systainers by putting the “T” between the catches. Problem is: Somehow you need tension / friction. And it seemed to me that having enough of a friction fit would eventually wear away at the plastic.