I've seen some trucks on various websites that used the saddle tanks from the 73-87 Chevy trucks and put the filler neck on the bedside in front of the rear wheel-well like on those trucks. I'm sure it wouldn't be too difficult to weld the filler door on there.
LMC carries a kit that looks like it is based on a tank out of a K-5 Blazer and the filler wouldn't interfere with the bed floor and the filler would be on the side of the bed.
