Going to share a technique I've used on a few things. Works best for plastic enclosures, but works ok on metal if environment isn't too harsh. Also, ok for LED, not so much for LCD but may work, it's quite diffusing.
1) Cut hole in enclosure bigger than display
2) place enclosure upsidedown on aluminium block (as a heatsink)
3) spooge hot melt glue into hole
4) press display into hot melt
5) spooge more hot melt to hold secure.
The aluminium heatsink hardens the glue flush to enclosure face but glue is transparent enough for LEDs and some displays.
The keypad will be fine. Maybe deal around inside of slot if using a textured enclosure.