Hello Robby, I don't know anything about the triangle tube water tank, do you have a link to a website??
As for the SF360, they are a very good hand-load boiler. My only concern is the Bitum. coal you burn... Your descriptions of how it burns in your TLC2000 certainly makes it sound like very good Bitum coal.. I'll explain what my problems were with burning Bitum in my 'Big Bertha' boiler
My Bitum coal liked to swell, get soft and stick together into a rigid sheet of coal. This caused the fire to burn out underneath the 'bridge' of coal, and I had several times where the fire would not be making any heat, the firebox appeared full, but when I broke bridge of coal, it colapsed into the bottom of the firebox, the coal was almost burnt out... I started going back to the boiler after an hour or so and manually breaking up the bridge.. this helped.
My Bitum coal had a lot of ash, and a low ash-fusion temperature. So when burnt at a temperature that would effectively heat water, the fire created lots of clinkers.. Part of this was due to the design of my firebox,, it had a narrow center grate, and 'V' shaped sides... so the firebrick funneled the hot ash together, forming clinkers as the coal burned... You shouldn't have this problem with the Harman firebox, it has vertical sides and a full width grate in the firebox.
My Bitum coal had lots of volitiles, and made lots of soot.. So I had to scrape the inside of the boiler surfaces every week or so.. Not as often as when burning wood, but the soot tended to insulate the surfaces of the boiler.
You mentioned in a post that you feed your TLC2000 on one side, let it get burning, then fill the other side.. you will probably need to do the same with the boiler.. otherwise you will get significant 'puff-backs' [minor explosions] in the firebox from the volitiles lighting-off after a fresh load of coal.
The surfaces in a boiler run cooler than the surfaces in a stove, so you may not get as much 'self-cleaning' of the soot as you get in your TLC...
As for locating the boiler in an outbuilding or garage, this is a very effective way to keep the dirt, soot and smells away from the house... If you look on ebay.com for outdoor wood boilers, you will find lots of sellers of insulated pex-pipe packages for tranfering the hot water into the house...
You will also find sources for water to water and water to air heat exchangers for use in your house heating system.. I use two water-to-water heat exchangers, one to tranfer heat to the hot-water baseboard heat, and the second to heat my domestic hot water tank.
I use 1" pex-al-pex tubing, in a sealed insulated double wall pipe package, I loose only 3*F in 150' of underground piping, from my boiler building to the heat exchanger in the house... Don't scrimp on insulating the pipes, it doesn't do much good to heat the ground instead of the house.
That's all I can think of right now... Greg L