How often do you haul stuff that fills the bed? I get anoyed trying to haul stuff when my tool boxes and spare get in the way. Adding a tank in the bed would just take up more room and leave less room to haul stuff.
My long term plan is a flatbed with a 40 gallon burb tank under the bed (between the frame rails but flush at the bottom). Then under bed tool boxes approx where the saddle tanks were, but not hanging that low.