I realize that everyone likes to minimize the use of metal in the construc-
tion hardware of their Tesla coil systems and I may get flamed mercilessly
for what I am about to suggest, but I have had no problems with it.
I simply make the secondary form several inches longer than what the coil's
length will be and just use the trusted ferrous-metal "L" brackets. I do
make
sure that they are small enough so that they will not protrude into the
bottom
of the primary and/or secondary coil plane. It seems to me that the
relatively
small mass of 4 small (say 2.5") "L" brackets would not significantly
affect the
magnetic field of the primary circuit interaction. And "L" brackets are
a LOT
cheaper than a large PVC flange! Flange mount does facilitate easier assem-
bly/disassembly, though, as long as you don't glue the secondary form into
the flange. :^o