I put one in my back patio last summer. I use an old grill cover so it doesn't rust, I imagine it would get worn pretty quick i I didn't have it one there.
Mine is wood burning, no gas. So the bottom and walls are all firebrick and I didn't mortar the bottom in, so any water that gets in seeps through the cracks in the firebrick.
Couple of recommendations:
1) Go with wood burning, gas is cheating :grin:
2) Def need some sort of cover, esp if any water won't run through/off
3) You need air in the chamber, otherwise you'll be babysitting the fire. I had to fix mine with an air pump that i have attached from underneath my gas grill. I run the air pump through a steel pipe that comes out in the bottom of the pit in the santa maria....now the coals/wood burn perfectly with little to no maintenance..