I disagree with the Gomog instructions for exiting the car. The easiest way (for me) is:
-Slide the seat fully back and open the door
-Put your right (for RHD) foot out of the car
-Put left (for RHD) knee towards the centre of the car and the left foot towards the door to get your left foot out of the car, pivot towards the door as you do this
-Slide forward a little
-Stand
No heaving, straining or stressing bits of bodywork involved and works fine with the roof up. It comes naturally to me as I was in a body brace for six months after having my spine fixed up and I was taught to get in and out of cars without twisting.