I used to do that, when I had a running station wagon and a 50 lb MTB. I took the bike to group rides 30-50 miles away a few times. Seymour Hope and Parke county IN specifically. No cushion, the ranch wagon had been used to transport lumber and the vinyl coating of seat backs & spare tire cover were scarred already.
I transported my 94 lb cargo bike last week in the back of a toyota camry. It was a 94 degree day, and my motor quit out in the hills, so I called for help. I thought maybe the controller had burned a transistor. I had to take off the panniers, the aluminum rack over the child seat shelf, the aluminum foot shelves: to stuff the rear of bike in the trunk. Then nylon straps to hold the front in under the tied down trunk lid.
Fortunately the problem was a wire pulled loose by my pants leg rubbing it. If I had been only age 55 or carrying reading glasses, I probably would have seen it. Then again my face was so sweaty reading glasses would have been fogged over by drops. Sweat doesn't drip in the wind of riding, but accumulated immediately after I stopped. I bent a flag terminal tighter and installed a plastic shield over wires to keep out pants leg, no more problem