One way to deal with the leaky front end of the coach is to make up a heavy curtain to draw closed or hang for the purpose somewhere back of where the holes through the floor and the dash are.
Perhaps run from behind the driver's chair to the vertical beside the driver's door takes care of all those places that may be leaking heat.
Floor to ceiling, wall to wall, cut to fit snug around whatever is in the way. You are trying to prevent air circulation, so if it is tight at the bottom, the little bit of gaps at the top won't be able to free flow. Or vise versa.
happy coaching!
buswarrior