Bucket of worms

I thought it would be a simple task to buy an in bed fuel tank to go into the bed of my new 2113 GMC 3500 with a estang encore bed cover. Well it is more of a task to find one than I thought. It seems as though when you look at the spec's for the tanks they show the body height and that does not include the fuel fill neck and cap. So I guess the search will continue till I can find something that will fit under my cover....I guess the fabricators do not take covers into account when designing these tanks....