Where to put components behing the panel?

Just temporarily mounted the components on the face of our panel. Now I have to determine where to mount the AHRS, remote transponder, ARINC, EIS, BACKUP BATTERY, remote radio, Main Voltage reg, Stby Voltage Reg and a Lightspeed Ignition behind the panel and between the panel and the bulkhead.

I would really like get ideas of how builders have squeezed all of this stuff in that limited area and how they've mounted the components. I'm thinking it will require poking some some holes in the bulkhead and/or building some racks. Ideas and pictures appreciated.

Jerry

G3X Touch component placement

Here is what I did for a full G3X touch system. Only item I do not have is the electronic ignition.

I had panel built by SteinAir with only a rough idea of placement. This took some head scratching but I am happy with this arrangement. Everything is sufficiently accessible with screens out.

-ADAHRS is mounted to back of left screen.
-Remote COM2 (GTR20) is on forward left part of sub-panel with connectors pointing down. This is the only box between sub-panel and firewall. I imagine you could do the same with electronic ignition.
-Rack in front left is for transponder (GTX45R). It can slide out of rack to right.
-There are no remote boxes in tail, only autopilot servo.

From left to right :
GAD27
Primary regulator
GDL51R (SXM receiver)
Backup regulator
GAD29 (ARINC429) on center rib
GEA24 (EIS)
GD40 CO Monitor
IBBS Backup Battery

Remote audio panel ( GMA245R ) is strapped to top of GTN650 rack.
Sub-panel cutout is for GTN650 (and connectors/wiring out back of GMA245R)

I built a small shelf (full width of the tailcone) behind the baggage compartment bulkhead, for the AHRS(s) and magnetometers. I was a bit concerned about magnetic interference from the should harness cables but so far so good.
I put a remote-mounted Trig TT22 transponder on the forward (toward the engine) side of the sub panel, fairly low. Easier access after the panel is in place. I also have some small stuff (engine MP sensor, etc) on the forward side of the sub panel. Don't forget, any large holes in the sub panel need to be reinforced.