re Communications in adverse terrain & conditions.
There is no specific type of Comms. that is an absolute to rely on especially with 4 wheeling.
Reason : Terrain - we are either on top of a hil (good) or down in a gully (bad), forests and bush suck the snot out of a signal, especially when its wet.
26 / 27 mhz (why 27 ??) antennae generally are that long they get bashed around as do any efficient HF antennae, 'cause they are long (and heavy).
The best results have been from VHF, both AM and now the new FM 4x4 Frequency approved units.
UHF (PRS) are also a good all rounder using gain antennae.
The HF SSB units (ie. Mountain Radio & 4x4 Approved) are fine early morning & evening, more often using wire antennae thrown up a tree, purely stationary. As long as atmospheric conditions are favorable, skeds can be set up with "base" stations elsewhere.
Through utter frustration of reliable Comms. and a long term involvement with SAR & oncall with Clubs etc., a lot of us ended up Ham Radio Operators, where we now have legitimate access to a far more reliable world of communications, legally.
Skeds can be setup for specific trips etc., and monitored via National Repeaters, and or local ones, and on either UHF or VHF, as well as having an HF option.
Others can be specially catered for via Special Purpose Repeaters that are placed in strategic positions for "convoy" access.
Have a think about the Targa Rally, its all run via a central location and repeaters.
Remember - there is NO reliable one stop option - especially Cell Phones.