Wiring for Espar unit and Four batteries

Hi,

Anyone put an Espar unit into their dodge? And what about wiring their truck for four batteries? I have a 2001 Dodge Ram 2500 24V, I am from Nunavut (Canada's newest territory, if you look wayyy up on the map you'll see it). Average temperature during the winter is -45 so a pre-heat unit would be awesome. Just wondering if anyone has put a Espar unit into their truck or anything similar? Also would wiring four batteries up be beneficial compared to getting two with a high capacity? I would simply add two to the existing in Parallel, hence keeping the same voltage but basically doubling the capacity. Any thoughts?

-Russ