bought the FT-2900R today, along with enough other stuff to get it installed, antenna, mount ...etc. I'm going to see if I can mount the antenna to the lip of the hood, and potentially mount the radio to the outisde of my (between teh seat console)... Alt antenna mounts would be the lip of the cargo door or to the front bumper. Can't have the antenna too high as tree limbs and stuff are everywhere ...where we ride in TN and other places I go. Waiting on stuff to ship and got to take the lic test soon.
Really good choice for a radio. You should get years of reliable use from it.
Antenna mounts-There is no perfect location, but the best is in the middle of your roof. Often not practical with trees and stuff.
Various lip mounts are good, and likely a lip mount on your rear lift gate will be the best compromise. Just remember every mounting option is a compromise.
For 2m only operation, you can't do better than a Larsen 150 antenna. It's just a steel whip that can take serious punishment. As a bonus, it's inexpensive. The whip part of it can be replaced for less than $20. There are higher gain antennas, but they are more complex, more expensive, and don't take abuse as well. Avoid the antennas with the little coil in the middle of the antenna whip. They get bent very easily.
If you are mounting on or near the roof, use a 5/8 wave antenna. If you mount somewhere suboptimal like a bumper or hood, you might consider a 1/2 wave antenna. It will be easier to tune, but the gain will be less. Again, it's all a compromise.
Regarding power, it's all ad hype, because either 1/4 watt will work or nothing will work. Occasionally, you need higher power, like for working a distant contact or repeater, but for trail coms, assuming everyone else has a well set up antenna, you need virtually no power. I leave mine on 5 watt output and can talk from one end of the Rubicon to the other. If I need to increase power, it usually means the person I'm talking to, did a poor antenna install. We have talked from the Rubicon trail head, to the Mt Diablo repeater (150 miles or so) on 5 watts. It's all about the antenna set up, so do a good job with this.
Good luck. And welcome to real ability to communicate on trail runs. Don't sweat the test.
KI6MIE