The last two pictures are of the heater I made. Couple of pipe fittings, an electric water heater element and an auxiliary water pump from a Mercedes. Heater element is a 3500W 220VAC which when couple to 144VDC puts out 1580W and heats the water up to about 90F with a moderate fan setting in the car. I have a control circuit to shut the heat off if it gets up to 190F but it doesn’t look like it is necessary. Total cost of the heater was about $100 and it heats the car in about 5-10 minutes. If I did it again I would probably go with a slightly stronger heater element, maybe 4500W but overall I am happy with it and it was relatively easy to build.