Shawdow, it isn't that critical on how you cover the tubes.I have pictures somewhere on this site of my single tube set up.
The negative rod only needs drilled to the bottom of the slots in the sides.They don't need to be deeper than that.
The Tube set needs to be set in a delrin base,so you need four sizes of countersunk holes.
1st hole would be @ 3/8 inch say 2 inches deep.This would be the water inlet.
2nd hole would be 1/2 inch and 1-1/2 inches deep.
3rd hole would be 3/4 inch and 1 inch deep.
4th hole would be the outside diameter of the cover of the outer tube,say 1 inch and 1/2 inch deep.
Your first hole would need to go into your chamber for the water to enter.
Anything in that set up will work fine.Donaldwfc has a nice drawing on here somewhere.
Don