I spent last week on the road traveling to FDIM 2014 (Four Days in May) and the Dayton Hamvention. As part of the road trip I operated quite a bit of HF from my small commuter car, a 2006 Ford Focus (84,000 miles so far.)
I have a short center loaded vertical using a six meter MFJ style Ham Stick (which has no native loading coil) which is then split in half and I have a Wolf River 10-40m coil in the center of it.
It tunes up fine 10m --> 20m with the center loaded configuration and gets out on 17m which is my primary day time mobile band. The problem is that it will not tune up on 40m which would be nice for evening QSOs. Wolf River recommends base loading but I want to try to center loading since it is more efficient but requires more inductance. At the conclusion of the road trip I decided that I wanted more band options so I went back to base loading.
Tonight I ran outside with my antenna analyzer for 20 minutes and documented the configuration for when it is setup with base loading. I am getting pretty decent 10-->40m coverage. It is almost a little to tall for 10m but it squeaks in.
This is pretty sweat because when I want to change bands I simply push the ring to the bottom and count clicks as I move it upward to the proper position for the band of choice. I can also slight turn/twist the tap point on the coil to tweak up/down the inductance. The MFJ Ham stick splits into two sections for storage. All of the coil and antenna sections have quick disconnect fittings so every breaks down very quickly.
I need to setup my pickup with a similar configuration sometime soon.
73 de NG0R