Plexiglass Form

The form I have the merchant says is cast. I used a hole cutting bit in the
drill press to cut a cap for the top and a 6 inch base plate for mounting.
Both plates will have a hole in the center but no wires on the inside of the
form. Is this an OK design or should I seal the holes completely. Also what
would be the result of evacuation of the form and putting in neon, any
adverse effects?     Steve