Diesel at $3.23 today makes me feel better, at least.  Still .60 more than low grade gas.
I have never (in 12 years) felt the need for an aux tank.  If I am running really low and the advertised price is more than seems reasonable, I stop and put $20 worth in,  Sure it is only 5 or 6 gallons, but at 10mpg with the trailer on it gets me to someplace with more reasonable prices.  The only exception was to and from Alaska when I filled as soon as it went below half, no matter what the price.  Petro Canada loves me, this I know.