Can I season a cast iron pan on a charcoal grill?

Maybe you are using heat that is too high. It really doesn't take that much. A 375 - 400 F oven will do the trick. Light coat of oil, heat for an hour. Allow to cool in oven. Wipe out. Upside down allows excess oil to drip out (use a drip pan)...but you don't need that much to begin with. There is no reason you could not do this on your grill. For the first few uses, wipe out and scrub with kosher salt to remove cooked on bits. Then give a light coat of oil and wipe out. Once you have built up the surface it is fine to clean with soap and water.

Yes, and it's a good way to avoid the smoke. However, the challenge is keeping your grill from getting too hot; if it goes above about 500F you'll be burning the oil off instead of polymerizing it on. So you need a grill you can reasonably hold at between 375F and 450F, depending on whose seasoning technique you're following. I didn't have a problem doing this on my gas grill in San Francisco (mostly because the hard thing was getting it hot at all), but on many grills it may be hard to control the heat.

There was an episode of Alton Brown where he seasons cast iron using indirect heat on a charcoal grill, but unfortunately that segment isn't on YouTube.

Some Serious Eats resources on seasoning:

http://www.seriouseats.com/2010/06/how-to-buy-season-clean-maintain-cast-iron-pans.html http://www.seriouseats.com/talk/2008/07/seasoning-an-iron-skillet-on-the-grill.html

Nobody I can find speaks of any advantage for seasoning it upside down.