..I use 30" of 1.25" solid fiberglass rod extending up out of the top of the mast upon which the I10k & Penetrator were mounted with a 5 turn CMC choke made from the coax, on a 4.25" circular former of gray pvc.
..The Penetrator "Wiped the floor" with the I10k until I fixed the incorrect radiator design (out of the box) then they were neck & neck to the valley below, some 40 miles from me.
..They make the same mistake Shockwave and the newer Penetrator do, it must be modded before you'll get the maximum 5/8 wave performance efficiency.
..Hats off to Avanti, designers of the Sigma II 5/8, the first genuinely pure and correctly designed 5/8 wave 11m base antenna.
---EDIT---
..One thing I left out, when I bought the Penetrator 2nd hand all but one top hat rod were broken off and when I tried to straighten the last one to a straight-up position it snapped off, so I ended up just adding about 8.5" of tubing to the top until it dialed in on the MFJ259B.