@Chris
Just getting back to this thread.
Sounds like the antenna is now tuned well enough, although removing powder coat between antenna mount and carrier and between carrier and tub for a better RF ground would be in order. Doing that will not require you to re-tune. Use tinned copper braid or strap, not wire, because RF waves travel on the surface not through the wire and braid has more surface area.
Conceptually, think of antenna mount grounding to the body/frame as providing something for your Tx radio waves to push off of, like a diver pushes off a diving platform. The more solid the platform, the higher and farther from the platform the diver can dive.
As for antenna springs, since you apparently have a decent tune I would leave the antenna and spring alone for now. Don't mess with success.
If you change antennas, my recommendation would be to ditch the spring and stiff 3' Firestik II and replace with a flexible 3' Firestik Firefly and no spring. (Wilson also makes a flexible antenna but no one I know likes them.) Or you could use a 2' Firestik II sans spring but performance will suffer somewhat from the shorter antenna length and because less of the antenna will extend above your jeep. [AFAIK, the shortest Firefly is 3'.]