Choke design

Hi all,
    I'm about 3/4 of the way through gathering the necessary materials
to build my first TC.  The secondary was wound earlier today at the
local motor shop, the 15kV -at- 30mA was delivered last week, variac and
mains filter will arrive any day.  The one part I will be missing is an
rf choke to protect the NST secondary.  After banging my head against
every search engine I could imagine, I still cannot settle on a design.
The web sites I've seen are recommending something like 26ga on a 2"
ferrite core.  Others seem to imply that I won't need that kind of
protection at 15kv.  Any discussion on this topic would be greatly
appreciated.  For the record, the rest of the specs are:
Secondary:  4.5" x 22.5" 25ga on ABS
Toroid: 3.5" x 17" Al duct
Primary: 10 turns 1/4" copper at 45 deg
NST: 15kv -at- 30mA (also have 12kV -at- 30mA)
Capacitance: .01uF -at- 20kV DC ( I know this will not last)
Spark Gap: RQ style in need of a fan

Thanks for making the fun possible for all us budding TC'ers.

Wayne Scott