Dear Click and Clack

DH is "on the road" sales.  He puts on more than 20,000 mi a year.  He is using the old family car that my budget paid for and has no savings in his business to purchase the next car.  Here is the queer part. ALL of his gas receipts show that he pays with $10 or $20 cash and takes $10 to $15 in change, buying gas $5 to $10 at a time all over the state!  When I ask him about this, he says he only puts in $5 at a time because he has the trunk weighted down with so much weight that he doesn't want to put more than a couple gallons in at a time to SAVE GAS because it would make the car heavier to tow! And he doesn't trust himself with a credit card. It makes no sense to me. His whole concept of budget, profit, cash, credit savings and his over-positive ideas about value and profit and time makes my brain spin more than an ADD brain does.  $5 cash each time for gas to save money - what is he doing?