One disparagiing note - don't expect to cut thru the cured CA adhesive later -- you'll have to cut away the foam around it.
I wrap servos with blue painter's tape - provides a little 'tooth' for the adhesive - then a pea-sized dollop of hot-glue to hold 'em in place. As Freddan said, hot glue makes later removal without damage a piece o' cake. That's at the home shop -- I also keep a roll of double-sided tape ('servo' tape, actually) in my field kit for a quick fix....tho in truth, I've loaned more of it out to others for fixes than I've used myself!
Silicon, I'd be cautious with -- some types of foam don't like it. A friend of mine used it extensively on a foamie 3D kit he built. Left it out in the garage to cure overnight when he finished building it, & when he went to get it next morning to take to the field, found basically a pool of sticky rubbery substance.
As with any
untried material / adhesive combination, best advice is trial it first on an unaffected area! I know you've heard & read that a thousand times....but it's said that often for a reason.