Running plumbing from the hotwater heater in the house to the garage is not an option. That would require about 75 ft of plumbing just to reach the garage. It would also have to be burried underground for during the winter. My option is to put a second heater in the garage somehow. Would have to put a dedicated pump just on that heater, fill it with water, and wire it to where it only turns on when the temp drops. That's why I kind of like that little 2.5 gal one I showed you guys. I would just change the water in it when I do my water changes. Best I can come up with for now. No way I'm running 70' of plumbing, and then another bunch for inside the tank. Requires digging a deep trench from the house to the garage, boring through the concrete in the basement to run the pipes out, and then boring through the very thick concrete under the garage up into the garage. All that equals a pain in the A. That's why I'm kind of leaning towards the tankless or a small tank heater. To start with though it will probably just have a few 1000w titanium aquarium heaters until I can figure out what I'm gonna do. I think it would waste a lot of heat to run a hotwater pipe underground in montana. Would be fine during the summer, but during the winter....blah! The water would be cold by the time it got there more than likely. Who knows maybe the titanium heaters will work well enough once the water is up to temp that I won't put in an external heater at all!!! 
 
The plan goes forth as is for now, and hopefully within the next few months there will be water in this thing! For sure it will be finished before winter as that's the main reason for this tank is keeping my fish a little safer during the winter. I will be constructing a new box for the 350 gal also if time permits before next winter. Going to revamp the whole thing. Might even connect it's filter in with the big tank for added bioload on both tanks.