I had thought of it and ruled it out. But you are making me think again. How stable is it extended out? I want to extend as far as only leaving 1.5 feet in. Are the rollers loose enough in the tracks that it would droop in that case?
I only used 4 rollers on each side and they were spread out about 16" apart. Depending how many rollers you use and how you frame it up, you can make it really stable.
I figured if the rollers and rails can hold up the garage door panels, they should be able to withstand a load while being rolled. For a weight test, I had nine 5 gallon water jugs filled and it worked really well. The hard part was pulling the weight.
Looking at my own garage doors there is a fair amount of slop between the rollers and the rails, not laterally but in the weight bearing directions in your configuration. Is this the case? The other concern is rattle noise when going over bumps. The closer tolerance of the bearing setup might limit this more.
Doug, thanks for the idea on this. Here is what I came up with.
This was my outcome. Works really really well!
I'm late to the party but this is really fantastic!!!! Well done.