Use a metal case and ground them.
I'm used an EPCOS EC 90 11 O (setting off voltage = 90 V) to use with 100 W - RF Power.
The line loss is verry good up to 500 MHz.
The SWR for the SW-bands are perfect, also on 6m and 4m, usable on 2m and not so good for the 70cm-band.
