webasto Airtop 2000

You can get one from the UK for around $840. http://www.melloronline.co.uk/Vehic...ne)_Single_Outlet_12v_Heater_Kit_41SK464.html

Here's a recent installation that is nearly identical to my installation method:
http://faroutride.com/air-heater-installation/

BigMac77:
You can only run your heater for 1.5-2 hours before hitting 12.2V? There's something maybe not right there. I regularly run my Webasto all night long (10-12 hours) and only have it lower voltage on my 105ah Deep Cycle AGM from 12.75V to around 12.4V. And that's usually with a little bit of fan, and my Engel SB47K fridge running too. Also, this is in an uninsulated cargo in ambient temps around 32-50 degrees.

In any case, solar is a good move. I used to have my house system charging solely from an ACR. It worked okay, but high amperage charging without a multi-stage charger does deep cycle AGMs no favors. Putting 200W of solar on the roof and using a 4-stage solar controller has me at 100% charge after 3-5 hours of sun everyday—when running the fridge, heat, USB, etc. It makes the whole system work so much better than using only an ACR/isolator and you stop having to be so concerned with electrical consumption for the basics.

@Hack Saw. Sorry I missed your post a month ago. I've had my Webasto gas furnace installed for nearly a year now. It's been fantastic and we've used it a number of times camping in 32-50 degree conditions in our uninsulated cargo conversion.

Also, make note that the voltage you read off of a meter while the heater is running is not indicative of actual charge state. You need to turn off all draw to the batteries and let it sit for 30-60 minutes to allow it to settle and give you true voltage, from which you can guesstimate remaining amp hours. When the heater is running the battery voltage reading is often .1 - .2 lower than with no load—due to the 1.2-2.45amp draw of the heater.