Having come back to tin bottomed/canvas tops after being away over long, it is the draughts and the way that the material flaps about that gives us the soundest sleeps that we have experienced in years.
So the very things that would probably annoy the hell out of us during the evenings, lull us into dreamland during the night.
no problems with sleeping at all and always have been warm in bed. It's when you are sitting inside on a colder evening with a glass of wine and cards/tv/book that the draughts can be annoying as they come up right behind the sofa backs. For even colder, winter camping though it is vital to block the gaps as the heater can only do so much! I am currently making draught excluders from old jumper arms!
We always have a couple of those fleecy blankets that you get in service stations (or Ikea) with us and roll them up in to a sausage shape to put along the seat backs - making sure that they plug the draughty bit where the struts are.
I have also bought some blackout curtain material (even though it is white!) and lined the 2 long curtains behind the seats with it. It makes quite a difference.