reconsidering "why not propane"?

[SapTsunami]

Looking to scale up to a 2'x4' arch and considering fuel sources. It seems the conventional wisdom is that propane is very expensive compared to wood-fired, but I just did some math that made me question that.

The dour view towards propane may be unfairly influenced by:
-backyard boilers using an inefficient turkey fryer setup that is uninsulated and sends most of the heat around the pot instead of into the sap
-the hassle of refilling tiny 20-lb tanks or getting ripped off swapping tanks at Blue Rhino
-backyarders with no RO concentrator who need to boil off every gallon, instead of reducing 4:1 before lighting the flame
-people who don't count their labor and consider firewood to be a "free" heat source. I heat my house with wood and I know it ain't free

I'm looking at this unit from Smoky Lake:
https://www.smokylakemaple.com/produ...-customize-it/

-Up front cost is comparable to a wood-fired arch
-quick startup and shutdown. 8 minutes to boil is a lot faster than anyone can build a fire. If I get tired I can shut off the burner and go to bed - can't do that with a box full of wood.
-easier for my wife and kids to operate when I'm not around
-I don't have a sugar shack, so more compact off-season storage is appealing

now the math. I estimate I will need to boiloff 180 gallons of 8% concentrate to yield 18 gallons of syrup. The Smoky Lake propane evaporator claims 9 lb LP consumption to boil off 10-12 GPH.
Total 162 lbs of LP over 18 hours total boil time. My local hardware store refills a 100-lb tank for $80.
That's $130 of LP cost to yield 18 gallons of syrup, or $2/quart.
For comparison, a cord of split firewood sells for ~$350-400 locally.
Total cost of LP equivalent to 1/3 of a cord of firewood. There's no way I could boil off 180 gallons of concentrate using 1/3 of a cord. That sounds like a good value to me!

Anything I'm missing? (besides the romance of tossing splits in the fire every 10 minutes?)