1.
If the toolbox is solidly bolted down, you should not need a separate ground wire (the toolbox should be solidly bolted down anyway, even with a ground wire it would cause static on your signal if it's not).
2.
You can bundle up the excess coax if you want (it's shielded wire, coiling it doesn't affect it), but I myself would cut the excess off of it (if it's more than about 7-10 feet extra).
3.
What is a Uniden PC86? I can find 0 info on that (did you mean PC68?)
I would think stopping by a truck stop you could find someone to help you with tuning the antenna (or at least have someone check it).
It's not rocket science however. Get yourself a SWR meter (they're like $15 on the low end), read up a bit on how to use it, and either get out a hacksaw or a Dremel to cut the ant shorter, or get yourself a spring or a quick-release mount or just a spacer or something if it needs to be lengthened. If it's 1.5:1 or less on all channels, then you don't have to do anything with it at all.
If it's over 2:1 though, then you may not have a good ground at the antenna, and would need to correct that first before you attempt trimming it.