Insulation - If you are going to try to heat your van, it is necessary to insulate sufficiently. Otherwise, the heat will just escape and have little effect. The exterior surfaces to focus on would be the roof and sides of the 'room', 'cuz these walls hold in and down heat which rises upwards. Curtains could be applied to the doors and behind the drivers' seat, to further contain heat and stop drafts. The floor should receive some consideration, but is not as important. Different methods of insulation will be discussed in a later series of articles; I'm working on renovating my own van, as this is being written.
Safety - This consideration is critical. If you are introducing systems that your vehicle wasn't designed for, you must take extra precautions. Have a fire extinguisher mounted conveniently. Use smoke detectors, use CO detectors, use propane detectors - whatever is applicable. Even consider having a fire escape plan to quickly leave your bed and get out of your van; it could save your life.
Some options available:
Left: This small heater is built extra tough with a metal exterior case, and the fan motor and controls well vented for long service. It retails for around $50 and puts out up 5K BTU/hr. Unfortunately, ya' gotta' plug it in to an 120 volt shore power source.
3/ Small Portable Propane Heaters - These come in both open flame and catalytic design, you know the little heaters for camping or small spaces. I don't care for these because of several reasons. One, the fire risk. They aren't really built for durability, they are easy to bump into and knock around; they have high temperature external surfaces. That could spell disaster in a small contained space, with yourself and pets moving about. Two, exhaust gases. These units are vent free, which means they use the oxygen from the interior space, and vent the exhaust gases into the same air volume. The one you breath and live in. There are too many documented examples of death, resulting from these units being incorrectly used in enclosed spaces, when the all-important ventilation necessary was compromised. The low cost doesn't justify the risk in my mind; I'd rather do with no heat instead.
4/ Compact Airtight Fireplace - Some people use small wood fireplaces, but I think they would be unpractical and unsafe. In the confined space of a 'mini' or full-size van, I can't really them working out. In a larger step or box van, with open spaces and clearances, for sure. They do use small wood stoves in school bus conversions, where there is lots of space. However, the smoke plume from the flue would not help your urban stealth mode, probably attracting the police or fire department. But used out in the country, way cool.
Left: Newport Marine solid-fuel microfurnace. Mounted on a fire-resistant panel, with a 3" flue, it's size is 16" high, 8" wide and 10" deep. Uses wood, charcoal briquette or coal. Retails for approx. $500, but there could be a cheaper version out there.
5/ Propane Camper or RV Furnace - If it wasn't for the prohibitive expense, this would be the way to go. You wouldn't be tied to shore power, and you would have safe heat anywhere. But, the cost. The cheapest brand new system I've figured out, would run somewhere around a $1,000 to implement, and would only work for a full-size van. The only system I could figure out for my mini-van, would run about $2,000 to install. But, you could take the system from your present van to the next owned van, reducing the extended cost.
Left: Atwood Everstar 8012-II propane furnace. The standard type RV unit, it produces 12K BTU/hr and it's size is 21" long, 12" high and 9" wide. Although it has a bulky size, it can be placed in cabinets with tight clearances, costs around $400 for the unit and draws only 1.8 amp current.
Two photos, to the right and above: Propex Micro Furnaces. If I was going to install a heater in my minivan, this would be my choice. Very high tech., very compact but very expensive ($800+ for just the unit). They put out around 3-4K BTU/hr, are very safe and efficient.
A system like this requires an internal furnace, exterior propane storage, gas plumbing, control and safety systems, and a house battery system for 12 volt system requirements. This is usually why you see them in vehicles which are commercially converted for van camping. It's a lot of processes to deal with, and unless you are very capable, probably best left for the professionals to install. You could be able to pick up a used system, but you would have to diagnose it's safety and operational value. Could be dicey.
Left: Platinum Cat Heater. Although the Olympian Wave brand is more popular, I would prefer this unit. It is vented, so the unit doesn't dump moisture and exhaust gases into the interior air.
Right: Force 10 Marine Cabin Heater. If I had a full-size van, this is the unit I would go with. It produces 6K BTU/hr and is 16" high and both 8" wide and deep. Retailing for around $450, it doesn't require a house battery system for electrical system power; a big savings. It is also vented, removing harmful exhaust gases and moisture via a 1" flue.
For my mini-van and my lifestyle, options 1 or 2 would suit me. If I had a full-size van, I would definitely consider option 5. What's going to work for you, you must decide. But whatever you do, please, please, please - consider safety first over saving money; option 3 is very risky! It's better to pile on a bunch of comforters, instead of risking your life. Think about it. Happy Trails!