I put mine several places on the RV-3 I used to own, but the one that worked best was under the empennage fairing, between the horz stabs. In that case, there were no lights, or trim servos back there to cause any problems.
The current RV-8 already has it's EDC mounted in the same place, though I do have some concern over the current that has to run to the tail position light. I haven't wired any of that up yet, so it's too soon to tell.
A couple notes about mounting it near the rear of the baggage compartment- If you have an aft mounted battery, the current through the battery cables will make your compass readings wacky. Also, if you stow anything ferrous in the baggage compartment, that may also mess up the readings. This just depends on how ferrous it is, and how close you put the EDC to the rear baggage wall.
Cheers,
Rusty