I too considered cutting some holes in my forward fuselage, but then I came up with an alternate solution. The posts lately regarding cracking in an RV-4's forward fuselage makes me think that hanging almost 400lbs of motor and propeller of the front of it means the stresses in this area aren't exactly benign.
My workaround was to create a wiring harness that could be completely removed from the aircraft. The key was putting two D-sub plugs at the end of the wiring bundle that connected the avionics harness to the rest of the aircraft. This meant that all signals (CANBUS, RS232, trim signals etc.) and their associated grounds travel through this plug. I also made other D-sub plugs for connecting the avionics harness to the power wires and ground wires. Devices such as audio plugs, light dimmers, low current switches etc. were connected using gold JST-SH (model aircraft) connecters. Everything was completely removable from every device so I could do all the pin crimping and connections on the bench. The only thing I had to do on my back was install some nutplates for the adel clamps and do the approximate wire runs (I performed my sub panel cutouts very early in the build).
In addition, I got some 4" thick cool-room polystyrene foam and laid it down on the forward floor. With the seats out and the foam on the forward floor, it really wasn't that bad for the amount of time I did have to spend on my back.
Before I moved ahead with this d-sub fuselage plug concept I checked with both Stein and a local Avionics Technician (who ended up performing my final inspection and IFR certification). Both had never encountered this solution before in a GA aircraft, but saw no reason why it wouldn't work. 75hrs in, it has been absolutely flawless and it gives me the ability to easily remove it and modify it in the future as I deem necessary.
In addition I made some other mods to make things easy for myself in the long run, such as a removable CB panel, conduit through the center tunnel (on standoffs and the floor is insulated with a titanium/ceramic layer on the outside)to allow future wire runs. The aft facing heater outlets are blocked off and the surface insulated (using pure merino wool laminated in stainless foil) to prevent heating of the conduit/wires. The side vents were opened slightly to ensure the heater airflow was not restricted. I also added plenty of other large cutouts in the panel to make installation and maintenance easier, for example I can remove both my whiskey compass and G5 by just undoing a few brass screws.
Anyway, hopefully this is some food for thought before you take to your fuselage with a die grinder.
Cheers,
Tom.
RV-7.
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