First, I don't think a plug-and-play antenna exists - they all need to be tuned to your equipment and mounting location. I believe the Firestick site lays this out in more detail than I can.
Second, I'm guessing you want to mount it on your front ARB bumper and not the rear. If this is the case, I think the 4 ft height will be fine even with a RTT b/c you have the large surface area of your hood. It is not ideal, but will be an acceptable compromise.
If you are mounting on the rear ARB, the height will be much more important and you will really need to get the antenna above the roof / tent as much as possible. Otherwise, you will not be able to get the SWR down to a safe range and you risk damaging your equipment when the antenna is not able to effectively transmit the energy from your signal (and you will have no range as a result).
Third, I think the biggest problem you will have with mounting on the ARB is getting it grounded. Without a good ground, your SWR will be WAY too high no matter how much you tune the antenna. It can be done though (I've got a 4ft Firestick mounted on my front ARB bumper), you just need to run a ground wire. I get perfectly fine reception and transmission on my CB given its inherent limitations (10-15 miles on flat open highway and 1-3 miles in really hilly forest areas).
I'm no expert, but I hope this helps.
