We have had an in bed auxiliary tank in our 8' bed trucks for over 35 years. Never have I connected the tank to the truck always used with a transfer pump. , as we also switched fuel according to season.
When RVing, on a long or snowbirding trip, Diesel gives long range(1100 mi. +) and the ability to fuel when and where we chose.
In our business season when we could not travel much I switched to gasoline to fuel mowers, gas SxS, gennys and such.
For us it is financially worthwhile as I have welded every tank and can commonly save $. 20-50/ gal fuelling .
A meter and water block filter on the pump solved use and condensation issues.