Far as I know, pretty much everyone either taped, glued or velcro'd the little bits and pieces in. IMO (I have little humility, so no humble opinion
) Hot glue or velcro are probably your best bet. Hot glue can be easily chipped away, yet holds thing securely, and with velcro, all you need to do is pull it off and affix opposite-side velcro to a new battery/switch/fan/etc. Keep in mind you're going to have to replace and upgrade little bits always, so don't use any fastener too strong unless it's on something that you can replace altogether.