lp tank size for gas fireplace, FL

can i use two external 30# tanks like on an rv connection for a direct vent lennox fireplace in FL?
or have to call a gas company to rent a tank what size?

In this state, all gas appliances like that have to be hard piped in with no more then 18 inches of flexable line and a emergency shut of valve within 4 feet of the unit. As far as size of tank goes, i believe there is approximatly 24,000 btu/lb in propane, and your Lennox fireplace will proabably pull a little more then a pound a hour. So do the math and then you can figure out how big.
There is approx 96k btu/gal.

I think my math is right, i wasnt a math major.