You need the radio, an antenna, an antenna mount and an antenna cable. First, you need to figure out where to install the antenna. Top spots on the H3 are driver's fender, like cbetts and Portager have; spare tire mount like F5 (and I used to have) and roof or roof rack. Each location will dictate the type of mount and type/length of the antenna. They also dictate cable length. Anything towards the rear get the 18' cable.
It is very important that your antenna mount has a good ground. You'll get this with the fender and the roof installations. With the rear gate you need to run an additional ground strap, which isn't a big deal. I ran the cable through the door, under the plastic and carpet along the driver's side, to the radio control unit (for the 75) under the dash. F5 says there's a good ground screw under the plastic by the subwoofer (if equipped). I just drilled a hole in the body for my ground.
If you think you may get a roof rack at some point I would just get a magnetic mount antenna for now and wait and to a permanent install after the roof rack. Something like:
http://www.walcottcb.com/wilson-little-wil-magnet-mount-cb-radio-antenna-p-395.html
I think the easiest permanent is the spare tire mount. For that I would recommend Firestik L bracket, 4' Firestik II, 18' cable. Mount and cable: Firestik kit:
MK-64A8A Check out the Firestik II site for good info.
You can also hold off and borrow my Midland handheld for that trip and we can walk you through the install. I don't have a mag mount antenna for it yet so the range is short but it works for the trails.
Here's my spare tire mount install. I recommend getting a quick disconnect to make it easier to install and remove the antenna.
Before you use the radio, be sure to tune it with an SWR meter. You can permanently damage the radio if you don't do this. If you're not sure what this means, don't use the radio until you work with someone that can help you. You can still do the install, just don't use the radio.