I’m also interested in adding a backup camera to my GT4 and came across this product:

https://www.ebay.com/itm/Porsche-Ori...pZ-ayI&vxp=mtr

It appears to be a simpler install (no wire splicing) than the NAV-TV kit, and it’s lot less expensive. It’s limited to a single camera so no front facing option. I found several positive feedbacks on eBay.

Anyone given it a try?

Thanks.