I've got a funny idea in my head to build an electric super cajon.

I love how the different surfaces and addition of some strings or a snare create such a super versatile piece of acoustic gear and I think I could make something even more bizarre and wonderful if I didn't worry so much about overall resonance and projection of the instrument, and could just cram piezos into every oddly designed section of the drum.

Problem is I've never done anything like this and am a pretty bad designer, so I thought I'd get lots of input here for designing it and then include a gratuitous "UG" in the drum's over-the-top paint job to pay credit to my favorite forum.

As far as I can tell, these are the things I need to consider:
1) dimensions, design, and material of the box *cheap since my prototype build will likely not come out that great)
2) a good type of harness for my piezo elements, so that they make great contact and pick up all those vibrations in the best, most articulate way.
3). A cheap DIY boost or preamp so that wimpy piezo signal will be proper instrument level (I'll personally need something simple and in a part layout form as I don't feel confident turning a schematic into a layout and am not a great electronics guy (I've built kits and such, but my complete DIY builds haven't had a good luck run) *also should be dirt cheap
4)interesting ideas for other useful percusive sounds. I think I'll go with the typical cajon snare, but figure I can amplify other more subtle additions as well. I'm not a percussionist or a luthier and have no real ideas about what would be practical and useful.

All constructive input is much appreciated. Or even feel free to tell me why it's a terrible idea. I really have no clue how good or bad of an idea it is, I've just gotten the idea of this creation in my head and it won't go away.

Thanks UG!
not sure if you want this on your guitar or as a drum which plugs into an amp seperately... or something else I, I may not quite understand?

I have made a stomp box which works amazingly well for how simple it is (it could essentially be a drum which plugs into an amp.) I started with an old speaker and built a basic box around it. I destroyed an old guitar lead and connected a wire to both the + and - wires coming from the speaker. the wire can then plug into an amp (use an old amp). the speaker works like a microphone except it doesn't have that dynamic range so doesn't pick up as many higher tones. I then put a plank of wood on top to stomp on (thinner wood has greater volume but doesn't have as deep or nicer sound so I found that happy medium.)

I learned all these things by jumping in and making it up as I went, so it doesn't look pretty but now I have an idea of how to make a better one.

that may or may not have helped but, I am after more details of what you want to do anyway, I am interested in your idea.
I wanted to make a stand alone unit, not something included in the guitar.

The observations about wood and finding a balance of volume and tone is useful. I think the front "panel" on most acoustic cajons is thinner. I was thinking of going 3/4 inch for the body of the box and 1/2 on the front panel, but I honestly have no idea what will and won't work.

Here's the weird rondomusic item that got my brain turning in this direction: http://www.rondomusic.com/product2892.html sounds a lot like the device you've developed.
yeah I didn't realise what a cajon was at first.

my brain works in metric but 1/2 inch (13mm) is about what I would have used for my speaker setup in the end.

yeah thats pretty much what I built, it looks nothing like that though. bulkier and more diy.