Hey Josh, If you can get one in your area, the DAP audio D7403
case is perfect for a small pedalboard in a live in hard case.
Although it's a little wider than you want at around 20". I'm in the USA and had to order it from Europe from a place called
Music Store .com. It's fairly inexpensive.
I built one not long ago for my guitar player friend, and used a much simpler design than mine that is really light weight.
Here's a couple pics of the case after I flipped the latch over, changed the handle(didn't have to but I already had a extra leather handle)
and put rubber feet on the bottom.
Here's the actual board, just a simple lean two design.
The four holes (you can see two of them in the pic above) on the ends of the lexan board, bolt into the rack rails
(that come with the case) that I sawed off and relocated where I wanted them.
A pic of the included rack rails below -modified and relocated.
I used the 3/8" lexan only because I already had it and it was free. Could use wood or any other suitable material instead.
I made this board at home with only a table saw and a hand held drill, besides the locking jack holes which were done on a
mill but could have used a hole saw for that.
The front of the board rest on the inside bottom of the case so no need for a center brace.
Just thought I'd throw this out there for some ideas.
And hope it helps. A few more pics of the board below.