The Sharman MB-400 mount is nice, strong and well made. Thats all you can say for it! Its four 4mm 3mm grub screws i doubt will hold out long, and the nice black paint coating is non-conductive - theres no ground path through the whole thing!
The 105ADT 3/8th mount didnt fit the 16mm hole in the MB-400. So, so carefull grinding, cutting and o-ring selection, and ive modified it to fit. Its attached to the car, but i feel that additional work will be required to create a usable ground path, probably straps from the mount to the bodywork.
Im going to test the antennas on it later using the MFJ-259B, and see what the whips are like, at the very least i'll be able to positively identify which is which. I still think a through roof mount is going to be best, although the whips are very long!