Perhaps something like the kit they offer here would be helpful. The kit seems like it would work and the bike bucket directions under "more" provide directions that I would think can be modified to work with crates if someone prefers that to buckets.

BTW, I have no affiliation with the web site referenced. Just thought it might be helpful to some here.

Edit: I forgot to mention that Jandd is also a good source for this kind of hardware. Scroll way down the page.