First of all, the whole 2K full blast vs 5k chillin debate was moot in this application. The 5K was running full blast 90% of the time. Attempting to heat the annex room and the tent seemed reasonable, and it did a decent job... until wind. When the weather was calm, it had little problem maintaining an inside temp that was 30 deg above the outside temp, and would even kick down. However, when the winds began whipping, what little heat the non-insulated tent could hold would be blown out. The heater was full blast during these times, and that inside temp would drop to 15-20 deg above outside temp.
I did notice that when the temps were in the 30's it ran fine with the toolbox closed; when the temps got into the high 40's, I got over temp errors. The last night I was out there, the temps were supposed to drop into the 20's. I decided to abandon the idea of heating the whole area and decided to bring the hose up into the tent with me and zip up the front door around it. When I first snuggled into bed I had the thermostat set for 24C (the display reads about 4 deg hot), and it did a fine job heating the much smaller area. Knowing that I was going to get blasted by northern winds later that night, I zipped up the north-facing window that I had been leaving open a crack for ventilation. Everything was fine, the heater had no problems at 11pm getting to temp and kicking down then up again like any other heater. I awoke to a freezing cold tent at 4am. Looked at the display, and saw it was a low voltage situation. I remote-started the Jeep, and proceeded to fire up the heater, which is super fun because the fan is now blowing arctic air into the tent. The heater once again failed to start giving an uncharted E-10 error. So I threw on my coat, and my go-fasters and headed out into the breach. The first thing I checked was fuel, sure enough, the fuel line was not submerged in the fuel. I corrected that problem, primed the pump, and watched for an eternity the fuel slowly make it's way to the pump. I fired it up again and all was well. I went back to bed, realized that I left the toolbox open, but said, "******-it". The tent began to warm up, but I did notice that the case temp never reached that last bar on the display. The heater ran full blast until my alarm went off at 7am.
Overall, the heater operated for as much as 14 hrs per day, and used about 4 gallons of diesel over four days.
What I'd do differently:
Shorten the hose lengths, the heater didn't need to be as far away as I thought it should be
Abandon the idea of heating the annex room AND the tent, I will simply place the hose where I am, or perhaps find a splitter
I extended the wires for the controller so it would reach upstairs and downstairs, but it didn't need to be as long as it is
Add vent holes for fresh air, the box was closed because it rained non stop for 1 day
Add a volt and ammeter to my setup so I can better monitor my secondary battery