[doctorknow]

A fire pit that is UL approved and/or approved for LpG should be fine either. However, things to consider in a Lanai is that do you have an enclosed Lanai or ability to shut windows? If so then you must consider the Carbon Monoxide build up with using the fire pit inside the Lanai. Also if there is a leak at the propane tank valve-Propane is heavier than air so it sinks and would be a problem for pets ...and of course any sparks from equipment etc...e.g., don't vacuum your lanai if you think there is a slow leak at the propane valve. You should be able to smell a leak as there is a sulfur smell compound that is added to the propane for detection. If in doubt as to a leak get down on the ground and sniff.
If you suspect there’s a propane leak in your home or lanai, follow these safety guidelines:

Extinguish all flames and sparks in the area.
Get everyone out of the area.
Shut off the gas supply value on your propane tank.
Report the leak to your propane supplier or take the tank to a retailer.
Remain away from the area until your supplier can check the entire system if tank not removable.

Also just a note of caution that if you leave your propane tank out in the hot summer Florida sun it will expand. Propane boils at -44 degrees fahreheit in the liquid form and when it gets hot it boils into a vapor. In the tank in the hot Florida sun the pressure increases in the enclosed space and the propane remains a liquid but wants to boil. If your tank is "old" you might want to have it checked for hydrostatic pressure. (or just swap it out using Blue Rhino).