Magnifier with Helical cap: Materials questions

Hello all,

I have just about nailed down the design parameters for a tabletop
magnifier unit utilising a helical cap which also functions as the
primary inductor. Due to the compact size, I am exploring options of
shielding the various components, and I have some materials questions.

First for the secondary: I had read in a few posts the mention that
thickly coating a winding with epoxy will degrade performance in some
way. Is this because of skin effect, or inductive interaction with the
material in the vicinity, (like lossy pvc)? My idea was to pot the
secondary in epoxy, with about 1/4" clearance between primary and

Secondly, for the cap/primary: I need to make a cap that will withstand
the tank voltages with only two plates (no series configuration to lower
voltages) and I have access to some thicker plastics, namely styrene,
plexiglass and vinyl. Does anyone know the properties of these materials
with regard to TC Cap use, esp. puncture voltage/mil, K, and
compatibility with mineral oil? I plan on using 3-4 sheets of 70-120 mil
material (1/16"-1/8") instead of 10-12 sheets of 6 mil poly, which is
what I have now. Of course, I will pot in oil, but I figured that 3-4
sheets would be easier to purge of air. 

Thanks for any help,