Remember: If SHTF, you have to sleep sometime. The magic number for 24/7 watch is 5 people. Small communities are stronger than small families.
Also (not applicable to SHTF) we will be experiencing more and more gas shortages as time goes on. Don't run to empty - and it's bad on fuel pumps to do that anyway. Possibly consider getting bigger tanks as well, a nice hedge against the retardation we are and will be dealing with.
Example: O.B.S. Fords can mount a Spectre F26D (38 gallon) in the rear to replace the stock 19 with nearly no modifications. They can sometimes mount a 32 gallon poly tank in the midship from a super duty with a lot of modifications. Total capacity: 70 gallons off of "stock" tank locations. That is some impressive range. Other combinations possible for most Chevy and Dodge trucks, new stuff though, I don't have a clue on because I don't touch new, probably SOL anyway.