I've got all garmin and a VPX. Keep the VPX closest to most electronics (if that's dash or behind seats). Although if you'd planning on physical buttons/switches on the dash, probably best to keep it under the dash. It's A LOT of wiring. If i did it again I would put the gsu behind the seats just to keep from having to run static, pitot and AOA to the dash. You could probably put the gtr20 behind the seats too. Would also make it easier to keep separation between coax and electrical. Gea24 is best under the dash.