just pretend it's a panel truck, I've always got around ok in them without seeing out any side windows

along the lines of what John suggested, back in the day there was an aftermarket [burb accessory?] heater that went under the seat, had it's own fan that blew to the rear, xtra heater hoses ran under the floor to it .... I've seen a couple, not available of course, but I have it planned to fab up something for the future panel
daily drivers don't hafta be "stock", just driven any old time regardless of the weather, if it was a garage queen you only drove in fine weather to show off you wouldn't have the problem .... or of course, if you moved outta the rain forest

Bill