First time seeing the dual stacks.... I like it...
About using the smoker as a warmer..... Proper built with air inlets (2) in the FB.... and proper sized exhaust... and proper RF plate and opening at the end.... and proper space under the RF plate......
All one has to do, to control the heat so it acts as a warmer is........ Cut the air to the fire 10-30% to reduce the heat output..... Then open the upper air inlet a bit to increase "flow through air" to the Cook Chamber...... VOILA...... instantly cooled down CC.... and the temp can be regulated using the air controls on the FB.....
The second stack in the CC at the opposite end..... I've seen them.... don't know how they help the heat air flow.... or why it would... The smoker is functioning as a result of convection currents... hot air rising..... differential pressure between the top of the exhaust stack and the inlets on the FB... (that , by the way, is the primary reason to have a very well sealed smoker)..... so, having one more stack could disrupt the delicate balance in the smoke/heat flow.... at least, that's my thinking.... could be wrong, been before, will be again....
these designs of smokers work VERY well and have attributes most folks don't realize.... Built correctly and VERY well sealed, they are efficient.... The second air inlet in the FB provides EXTREME control over the smoker.... most folks WILL NOT take the time to learn how to operate a 2 air inlet smoker..... I think they are afraid to burn wood to test it out... tweak the settings... etc..... wood must be darn expensive where they are from...