Cut a piece out of a big truck inner tube and stretch it over the rim so it's a snug fit in the drop center section. Bicycle rims used to have a band like that to prevent the spoke nuts from chafing inner tubes, on the ones I rode about 60 years ago, anyhow!
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!