I would go with the bigger tank as well. The 500 lb tank should be big enough. They will come out and fill it, so you have to locate it where a big truck with a hose can get to it. You can probably sell your used propane tanks back to your supplier. Fire them empty first of course. Driving around with two 100 lb propane tanks in the back of a truck can be a bit dangerous. People look at you funny when you go through the drive through to order a Coke/Pepsi and you've got these two towering silver tanks sticking up over the cab of your borrowed truck.You do get respect at red lights though-people don't run the yellow when they see you coming.