I think I have one of those Tempur-Pedic pillows or cushions that I got my wife when she was pregnant. They are very firm and will support the forend (with my hand underneath).

As far as securing the milk crates - I think that I'll just bolt them onto the bench. If I recall, the benches may have about a 1/4" gap between the planks. This may be enough to get a long u-bolt around the edge of the crate and down through the wood and secured underneath.

I love these projects within a project, within a project, etc....

Thanks!