Boy, some mean folks from the comments.
Lighten up.
Folks have various GOOD reasons to want a little more distance. Vehicle manufacturers just don't get it by putting in tiny tanks when towing nets you a measly 200 miles or less distance.
Myself, even with a 35 gallon tank I HAD to short hop multiple times at 125-150 miles because I was trying to prevent the need to stop for fuel in BAD places or sometimes EXPENSIVE states with super high taxes.
Those short hops cost me a lot in TIME spent looking for gas and TIME in getting to stations and TIME getting back on the road. That time wasted for one trip was SEVERAL MORE HRS EACH WAY.
I fixed that by buying a 15 gallon "landscaper" tank.

Fortunately for me, a local hardware store had a discontinued NOS tank (manufacturer went out of business) in stock for a bargain price of $100.
The one pictured above is made and sold by a different company but is the same design but costs a lot more than mine.
You can find it
HERE for $215.
I added a electric fuel pump and a filter and mounted it to a couple of 2x6s for stability and other stuff I put in the bed keeps everything in place and doesn't move one inch.
With the pump, it takes about 10 minutes to empty and I can just pull off the road at any convenient parking lot or rest stop at MY pace.
I now can go as much as 400-425 miles before thinking of looking for gas..
Skipping over entire states when I want to, PRICELESS.. :B