couple threads but I think there have been more
http://forum.driveonwood.com/t/building-a-wk-gasifier-for-harsh-winters/421
You pretty much sum up the main issues with driving in the winter with your above post. However also consider water freezing in your cooling rails if the slope isn’t that steep or you have a large cooling surface area. In most cases your pipes will just freeze and only 1/2 or less will stay functional by the concentrated warm gas flowing through them. Also hay filters (wet filters) will freeze and take time to thaw (or not). I remember one year I had to bypass 2/3 of the cooling rails so that I would have enough heat to thaw the hay filter, something to also keep in mind.
As for the other problems there are temporary fixes but ultimately your “southern gasifer” will need to be redesigned for a cold climate if you want to drive reliably through the winter. First is removing the condensate tank you won’t need it. Plum the cooling rails directly into the hay filter and the hay filter does double duty, i.e bottom 1/3 as condensate collector and top 2/3 as filter. That solves one tank freezing. Hay filter will need to be drained every shutdown and I recommend min 2inch drain without a ball valve. Ball valves will freeze solid at some time and be a real pain to work with. a tennis ball blocks perfectly a 2inch metal pipe just need to make some type of external fixation device to keep the tennis ball in place. This has been working for me and is cheap/easy to repair if need be.
Hopper condensate tank. I’ve had best luck with a regular 5 gallon plastic bucket with sealing lid like what you can find at home depot for paint ect. cut a 2 inch hole in the lid and use a shower drain upside down with gasket your 2inch inlet pipe then it can easily be connected with a 2inch rubber coupling. This tank will be removable from the gasifer with 1 hose clamp and easily replaceable. the plastic gives some insulation and i’ve never had one freeze while in operation. This also needs to be emptied every shutdown. however if it is forgotten then one can remove the entire top off the bucket and the ice popped out, lid replaced and back in business, these do not seem to crack if frozen.
so now we have removed one tank (condensate), and solved our freezing issues in the other two (hay, hopper). couple last things.
Plumbing under the truck should be abs and connected with rubber couplings/hose clamps in short enough pieces that they can be removed and inspected/cleared. Frozen water likes to accumulate down there and may eventually cause obstruction (had this experience) very handy to be able to take the pipes off and place in a warm place and allow the ice to slide right out this does not work if everything is joined by abs cement.
you may have issues with wood freezing to the sides of your hopper depending how high your hopper is/ if its past the roof line of the truck. this can be handled by either insulating the outside of the hopper or by putting in a metal screen on the inner side of the hopper to prevent the wood from touching the sides (both have advantages and disadvantages. What I have done is make a heated hopper that the wood gas flows around works well thus far.
this is all well and good but you need suggestions on winterizing what you have now.
- Insulate your wood hopper to prevent freezing of the wood to the sides and insulate the condensate tank under the truck the 2inch rubber cap will be good, just need to drain every shutdown. Carry a rod so you can punch out any frozen blockages if needed in the outlets. All outlets should be metal to allow for external heat to be applied.
- take out the Screw type plug on the hay filter (I suspect this will freeze solid and will be very difficult to remove. replace with a rubber cap and hose clamp. Personally I think the gold balls is a bad idea they will freeze into your block of ice, just leave as is.
3)the hopper condensate tank is the biggest issue at this point. personally I’d just drain it as usual and let that 4 inch stay frozen for the winter. May want to look and see if you can retrofit the hopper condensate tank that Described above for winter use only.
One other big thing. When thawing metal pipes or valves with a propane torch etc. make sure the valve is closed or else you can get some pretty exciting results very quickly 
if you need pictures I can share some