I got some MDF & made a base that fitted into the floor of my car on the 60 split side. I then screwed in a block the same width as the front dropouts & stuck a QR through it.
At the back, there's 2 blocks that the chainstays sit on, with holes in to pass some webbing through & secure the rear of the bike to the blocks.
I plan on doing a few refinements to this at some point, as the new bike is slightly taller at the front & so only just goes in – I need to lower the QR mount as much as possible.
I could post some pics if they weren't stuck on my teeny phone SD card.
When I get a car with a taller roofline, I'll be doing the same thing, but stickin the QR on a rail, so I can bolt the fork in at the boot end, then slide the QR assembly down into the car on the rail before clipping it secure. Then the back fastening would be via a QR as well rather than blocks supporting the chainstays…
EDIT – this is obviously with the wheels off, which I stick in wheel bags to keep the car clean.