Personally I would get PCI to do it. They will get you set up with the correct ant. and tune it for you. Just tell them that you will be on Weatherman most of the time and they will optimize the setup for that Freq.
We run a permanent install in the truck but also carry a handheld in the door. That has come in handy more than once when the CoDriver was out of the truck directing the extraction of another rig. Just my 2cents.
Ours our set up with a PTT button and wired helmets so we don't have a handheld mic flying all over the cabin. That might be overkill for your first round of events but if you like the program, which my guess is a LOUD HELL YEA, then you will get there in time.
The Lowrance GPS allow for a very high number of points and detail that make if very good for this application. Having hold points marked for support, markers and cautions on trail all make for a safe fun event.
This is an example of a file Matt did for me for the "La Carrera Del Norte" 500 last year, and you can see routes, alt access roads to the route, road intersection, etc etc. Its just all real handy. The fun run files are set up a little different, and include cautions based on pre run info. VERY VERY important because a nice wide road can have a hidden washout around a bend that could catch you out without the advance notice.
Been on quite a few adventures with these guys and can't say enough about the support, good attitudes and fun times.
Grant