I build an avionics or electrical rack between the firewall and the sub-panel. The rack in the forward e-bay ahs the fuses, regulator, SD-8 components, ground farm, and the GRT AHRS. So far, it's working really well and I have nice access through a couple access panels forward of the canopy.
I mounted our AHRS in a similar location to Jim - seems pretty standard for RVs and easy to get alignment right.
The Mag I mounted in the left wing tip - it works ok and was the 'recommended' location when I installed it, with 20/20 hindsight - I think Jim's location is better, much less electrical noise in that area compared with strobe, nav and wing wags.