In this circumstance, I was fortunate that the second time was the charm. I really didn't want to have a third go at building this thing.
Anyway, you can see the sled is done and the heater is installed in it. You may also notice that the new heater has a great deal less surface area than the original heater core. The new element is supposed to use 1500 Watts of power. To put that into perspective, that's the amount of power you're average hair dryer puts out, or 200 Watts more than your average Amish fake fireplace for that matter (yep, a hair dryer is more powerful). So I'm a bit concerned that it will actually warm the cabin adequately. Time will tell.