A water bowl .... lol. This of course depends on what you are using for an enclosure. I find with using tubs, a water bowl does the job fine on it's own.
I use a similair technique to the foil. I covered the screen on my 40g glass tank with clear plastic vinyl from Wal-Mart sewing dept.. It is on big rolls and they will cut it for you.
Covered 80% of the screen and can slide if I want to open it more. That and a big water bowl do it great. During shed I spray the Aspen bedding to bring up the % to 70 and it holds humidity like a champ. No more maintenance than replacing water every couple of days with fresh.
If you really want to have a easy to maintain enviroment that hold humidity and temp well than I really recommend switching to tubs. If your gonna keep it in a tank than theres really no need for an automatic mister, just cover the top with something and keep tinkering with that till you get what ya want.