Where to install GDL82 in an RV-8?

On my RV-8, the transponder antenna is adjacent to the leading edge of the left flap. Haven't taken the front cockpit floorboards out yet to see if that's a good place, but seems like a possibility. (The back seat floorboards are all pop-riveted in, and beside, you'd need access to the unit in the future.) The GPS antenna might go atop the aft fuselage next to the baggage area. And access behind the panel is only a half step better than atrocious.

Yes, I know this is an RV-8 specific topic, but I'm hoping that there's a better chance of getting an answer if I post here.

Ed

Transponder antenna not changed

Ed
I do not have an -8 and am not sure of the crux of your question but the transponder antenna is not replaced, the GDL 82 interfaces to the existing cable that goes to the existing transponder antenna. There is an additional GPS puck that has to be mounted and in my -7 I just put it on the dash.

The easiest installation is if you have space near your existing transponder so that there is only a short coax cable from the transponder to the 82 and the existing coax to the antenna can be plugged into the 82. The 82 with connectors and cable bend is a bit longer than the GTX 327 that I have and I mounted it on top of the 327 tray.
Figs

Like Figs I do not have an 8 either. So forgive me for adding comments that may not address the specifics of your layout. As Figs stated, you will use the existing transponder antenna. If you are able to mount your GDL82 near your existing transponder unit you can literally unplug the coax from the transponder antenna and plug it into the GDL82 transponder antenna IN connector. Then run a new coax from the 82 transponder antenna OUT connector to your transponder. The only antenna you really have to install will be the GPS antenna and its coax. That coax will need to be a minimum of 6.5 ft long. the additional length of coax can be coiled up and zipped tied anywhere behind the panel. If you build your own coax note the type of connectors required (BNC and TNC). Because of the location I placed my 82, I could have used a 90* connector on the back of my unit but did not have one. I also placed my GPS antenna on the dash just in front of the canopy brace (for a slider). As for where the unit itself is mounted, it would be best if you can mount it as close to the transponder as is practical.

Having built and worked on several rv8s I know there are lots of places to mount stuff, if you make them accessible.
Under the floor behind the foot wells is a great place if you make the floor removable. You can bond mounting structure right to the inner fuselage. I have used pieces of Deleon bonded to the inside of the structure, with JB Weld or 5 minute epoxy, to attach to, since you can drill for a machine screw and screw directly into it with out the need to tap threads. It also acts like a fiber lock nut holding the screw. You could also bond aluminum brackets. This precludes the need to drill holes through the skin.
Under the right side cover just in front of the spar is also a possibility.
You can remove the front seat and mount stuff on the side of the structure there and still have access or even on the bottom of the seat pan itself.
behind the baggage compartment, if you span the longeronns with a mounting plate like the elt mount that vans sells.
You could mount it to the bottom of the front baggage compartment as long as it doesn’t interfere with the pedals
Maybe even on top of your radio or transponder right behind the panel if there is room.
Always check for interference with the flight controls first and don’t forget about getting the wiring to the area you select
Good luck.