I have had, made my own in bed 55 to now 85 gal. in bed aux. tank since 1984. None have been plumbed into the truck Always used an GPI electric pump for transfer with a Goldenrod water separator filter.
Aux. tanks do have water condensation issues when they are not full. The water separator filter has saved us many a OEM fuel filter, and I just dry them out and reuse them.
Our reasoning for not plumbing the aux. into the main, is for filtration and in boondocking season and summer season to switch to gas from diesel to fill mowers gennys and such. The truck became a filling station. Gas cans a thing of the past. We buy fuel when and where we want, at the best price.
