Gasser - The drip tray & pan come out pretty easy, so I dump them a few times a season. Otherwise, the ol' gal only gets a 'spring cleaning' where I scrape everything down.
WSM - Not much of anything on the interior body walls, but the cooking grates get brushed every cook. I wipe the rim of the midsection with paper towel while it's still warm because it'll develop a layer of gunk that'll have the lid stick. Other than keeping the outside looking clean & shiny, that's about it.