I drive a coupe which has made it challenging to step up to 50cc like I want. Its probably better for my wallet anyway...
Anyhow...Im able to put my rear seats down and slide planes in through the trunk. After that got old, I just started placing them on the passenger seat, with the seat laid flat which was much more convenient.
I also carry my planes to work if I plan on flying after. I just take a large contractor bag cut open, or a sheet/blanket of some sort and lay it over the plane while parked. Keeps people from being too curious!
If you were a really dedicated flier, you would do what my flying buddy does. He transports his 50cc planes on the roof of his car! I can only imagine the looks he gets. I guess im personally just not that serious about the hobby!

The kicker is his wife has a big SUV. I guess we all know who the boss is huh!