Without being scientific.. they sell propane tank warmers on Amazon. So you fire up your genny, then plug in the electric tank warmer. and you're GTG.
I'll be scientific. There's some good information here:
And the other thing to consider is the heat of vaporization of propane, which is 184 BTU/lb:
The propane tank heaters I can find are all 120W. That works out to 410 BTU/h, which means they will vaporize 2.3 lbs (at 21660 BTU/lb) or 48,264 BTU of propane per hour, based on their heat alone. That's an improvement to be sure. A 20lb tank vaporizes only 24,000 BTU/h on its own at 60F, and that number drops to 7,500 BTU/h at 0F. But we can't just add these two numbers together to see how fast the tank will vaporize, because the heating blanket also insulates the tank from the outside, so I would expect to get something better than 48,246 BTU/h out of the tank, but not necessarily as much as that plus 24,000 for example.
Looking at the US Carb table, that heater can vaporize just a little under the amount of propane consumed by a 5000W generator at 50% load.
So, it buys you a little.
An 8000 W generator at 100% load consumes 160,000 BTU/h. Your propane heater blanket doesn't have a chance at keeping up, even in the summer.
This is the brand I have.What I'd like to know is how a 20lb tank will react adversely as opposed to a larger tank?