The load spreader bars that were originally used on Corvair air cooled engine valve covers make a huge difference in how well a stovebolt cover seals. They also prevent the distortion of the sheet metal in the area of the bolt holes. Clones of the Corvair spreader bars are available from most of the specialty auto parts people like JEGS and Summit. I like to use Permatex Super 300 brush-on sealer. It stays flexible and isn't nearly as messy as RTV and other tube type rubber sealers.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!