Rogertre, I was in a very similar situation to you this March. Transferflow makes tanks for gas and diesel, and yes...they are very expensive. I was going to purchase one, but they could not get it to me in time for my trip (Seattle to Orlando). So I ended up getting 2 5 gallon cans.
You're getting a new truck in a couple of years as well as switching to diesel. So it makes financial sense to wait on a big purchase like that. Maybe the gas cans, or something else cheap can hold you over.
We pulled in to a campground in California that was supposed to be open...but there was 2 feet of snow on the ground from a recent storm. I had been on E for about 5 miles at this point and we could not find a gas station. So the cans saved our butts because we drove something like another 30 miles before we found some diesel. After that we ended up only driving as far as one tank of fuel would comfortably go in a day.
Moral: You can work it with gas cans...but it is not fun. Especially if, like me, you start getting twitchy after the needle gets below half a tank.