I have a similar issue where my 2001 4runner has done the "i want gas" now thing so if I'm going somewhere new I carry a 6 gal in between my two batteries. You can see in this picture where it drops it:
I put it between the batteries so I still have propane plus batteries plus a little extra gas. At worst the extra gas gets me another 60 miles with the trailer which is plenty normally to find gas. If I'm really in a bind I drop the trailer then I can go another 105 miles...
I don't even strap it in; it fits so tight that I've never had issues with it even off-road. If I get into an accident I know the fuel will depart most likely but at that point that is probably the least of my problems.