DUDE. So glad you've cleared a trail this far. I'm after exactly what you're after - single connection to rack when mounted, clean water-tight and 'invisible' capped end when the rack is off. Been chasing this for over 2 years now.
Completely against drilling holes in the roof. However, given every other option that's been suggested or that I can conjure, I don't see any way around it.
Soooo...the best thing I've found is aviation connectors, particularly one with a 90deg bend. I haven't proceeded with the rest of it as I haven't had time to suss out the headliner removal w/o damaging it to run the cables to the underside of the roof. But...using this -
Amazon product ASIN B07B7LTQR6
- the elbow is on the rack end of cabling, with the roof end being the flat bit with the water tight cap.
Caveats thus far is the cap will need a dab of silicon due to the cable stay being connected thru the cap (small gap there) and the elbow is a split body affair requiring some kind of full sealing - perhaps silicon, or very large adhesive-lined heat shrink to wrap the body of the connector with.
The position of the pass-thru is centered at the rear of the roof, yet still underneath the rack (for protection and security), with the elbow facing rearward. This is so that all cabling on the rack can be routed to the rear-center of the rack, and straight into the elbow. Facing the elbow forward would require the wiring to loop rearward then back forward into the elbow.
Remove the rack and you just have the small, flat end with the cap for a very low-profile and nearly invisible capped off connector.
I can take pics of the connector (just placed for referrence) on the roof for an idea of what I'm talking about.
This fitting has an IP20 rating.
The 2 means protection against ingress of solids 12mm across.
The 0 means zero protection against water ingress.
You're 100% relying on whatever sealant you apply to the fitting.
There doesn't appear to be any seal in the cap, and no seal on the threaded coupling, or threaded connections.
Sealing it reliably and cleanly in a durable way could be a challenge, particularly if it's something you're going to disturb with removal of the rack.