Is it possible to use a car port for the radials with a vertical antenna?

If you are suggesting using a metal structure as the radials (aka the ground plane), then give it a try. I know Hams who have used an AA magnet mount antenna on a refrigerator top and even cookie sheets in the house in order to use the local wide-area repeater that operates at just below 147 Mhz. They couldn't make the connection with the antenna mounted on their 5 watt handheld but could with the more efficient mag-mount mobile antenna. The name of the game with Ham Radio is have fun and experiment to see what works, so why not try it with the others if they are built with removable antennas?