Here's some of the things I used and am very happy with:
Measure the signal with this:
Mcbazel Surecom SW-102 Digital VHF/UHF 125-525Mhz Antenna Power & SWR Meter
Here's a great antenna that is resonant on GMRS and will also work for 2M/70cm HAM. It's also spring loaded which is great for what we do:
SS-680SB Mobile Antenna, 2m/70cm, UHF, 27"
Here's the antenna mount and wire kit I used:
Deluxe Mobile Mount Cable Assembly RG-188A/U 9.9 Feet SO239 Base PL-259 Connector
www.hamradio.com
Great thing about these is that the removable adaptor allows you to pull through the smaller foam covered passthrough higher up on the driver side if the main path is obstructed.
You may need the longer kit depending on where you are mounting the radio. I have mine mounted overhead on a MOLLE panel with the head unit mounted on a ram ball mounted on a VECTOR bar.
I found a rare earth flat magnet that I mounted in place of the microphone clips so I can simply slap it back overhead on the MOLLE rack and it's always close to my reach. I can also stick it to the vector or anything else in a pinch. Works well. Pretty proud of this hack I came up with actually.
I'll try and take some pics this weekend of my setup and post them up.
If you want to jump on a call and discuss anything PM me on here and I'll be happy to help you out with wire paths etc.
Hope this helps.
-Dan