John Adamz wrote:I'm guessing you are likely on a very limited budget like me. What type of material is the J-tube made from? Lengths of feed,burn/riser? Is all but the feed tube inside the tank? A 3" system is very hard to get to work except for just a little rocket stove. Sounds like a 100 pound tank. Is the tank about 14x46"?
Here's a few ideas.
You need to match the J-tube size to the exhaust duct. Preferably go to a 6" J which the tank would easily support, or as a least desirable option a 3-4" exhaust. Your draw is being slowed way down by the larger exhaust, and the large space between the riser and the inside of the tank. Although it's a 3" riser your top gap is maybe a bit small. The burn tube needs a lot of insulation. In a pinch you could use sand or better yet cob, and riser needs more insulation as well. An 8-10" duct pipe around it lightly packed with fiberglass insulation could work.
Having the exhaust go out the side wall (Even a dryer vent outlet might work) on the down wind (leeward) side of truck could also help.
Without mass you have to keep a fire going all the time to maintain any temp unless you well insulate the interior space. If you could use any kind of mass maybe a barrel or 2 of water would be better than anything. Getting the water heated is a bit of an issue to keep it simple and SAFE!
These are a few off the wall ideas to give you a place to start.