Here's a thread that is currently posted. Board Member - tdave00 (Scroll down till you see his post) shows how another Board Member - SatcoJim did his fuel fill in his fleetside bed. This is nice:
http://67-72chevytrucks.com/vboard/s...d.php?t=277343
He shows his fill in the middle of the bed, probably a fuel cell but I am sure this could work with the blazer tank. Be creative.
Here's a couple of other ideas for fleetsides. I'll track the threads down.
One had the fill cap in the rear D/S Stakebed hole with a Cool Cap from Air Ride Technologies
Another had a flip down rear D/S Tail Light.
Another had a fuel neck fill coming through the rear D/S fender