I have done the shop vac thing and it did get the fire nice and hot but it is loud and annoying. That lasted about 20 minutes before I unhooked it. Don't know how well it would stand up to running for 12 hours straight. Can't imagine that you would get too many hours out of it before it ceases up on you. Restricting the air going in might help slow it down. Or, put a hole or a "t" in the output line before it goes into the evap. to slow down what is going in (release some pressure before it gets to the fire)