Propane is fine if you know what the pros and cons are and you are willing to accept them.
It will work good off-road but you have to keep in mind how long the trail is.
There won't be a propane station out there.
The actual mpg will go down. Even though the octane level is higher letting you turn the timing up, the btu's produced are less so the mpg's go down. If you build a high compression motor to only run on propane (and e85) then you can reclaim the lost power.
Some states/counties are now taxing propane for use in cars so the cost savings is not what you think...and the loss in mpg.
But they are very simple to install and no electronic parts.