The Marine industry has quite an assortment of heaters, coolers, and stoves that are easily adaptable to your "land yacht". Do an internet search for "Marine Diesel Heater". What makes them attractive is that you already carry a plentyful supply of fuel with you. Here are some examples:
http://www.impactparts.com/AAH/
http://www.kuranda.co.uk/html/dickin...l_heaters.html
http://www.dickinsonmarine.com/shop/...es-heaters.asp
http://www.espar.com/htm/applies/trucks.htm
http://www.sigmarine.com/our__product_line.htm
See the world from the front seat of a Volvo 610.