Every time I have gotten coverage on a land cruiser they have specifically stated that off road is not covered. Though I am not with any of the " big 5"... probably
Just a heads up to anyone whose insurance agent says that off-roading is covered - get it in writing. From what I've seen it is explicitly excluded on policies.
However if you're on a established "ROAD" albeit dirt and weren't driving on it with the intention of off-roading, you should be fine...but don't quote me on that. Coverage varies, but I've seen this get people coverage for stuff like this.
I think this is very state-dependent. In Colorado most/nearly all the "off-roading" is done on actual county roads. They are legitimate state or county maintained roads intended for registered vehicle travel. They are, therefore, simply roads and insurance coverage is the same as if you were driving down the highway.
If you're in a state like Texas where most all the land is private, that's probably not a road and coverage may not apply.
Obviously, don't take my word for it and check your policy to be sure, but once I understood the whole road/not a road thing it became much clearer.