Look familiar brad?
I was getting around to making and testing that design of yours but only got the first set of code done for the CNC. Still need to make the code for the rest of the passes. The only problem I am seeing is sealing it. Might have to go with 2.5" wide material instead to add a few screws in the sided in the middle. And maybe go with 3/4" thick material and make it 1/2" Deep and 3/8" wide channels. I been having pretty good luck with deeper narrow channels.
If I only had the time I would do a few up. But looks like I woun't for a few months.