RedirectMatchで半角スペース「%20」を-に変えるにはどうすればよいでしょうか？

RedirectMatch permanent (.*)\x20(.*) $1-$2
RedirectMatch permanent (.*)%20(.*) $1-$2
RedirectMatch permanent (.*)'%20'(.*) $1-$2
RedirectMatch permanent (.*)\x20(.*) $1_$2
RedirectMatch permanent "(.*) (.*)" $1-$2

全部だめ orz