I've got a JAZ (I think bought it 8 yrs ago,it's black)16 gallon.It only holds 12 gallons w/foam.I mounted it under the bed where the spare tire went,used a 4 1/2" hole saw drilled a hole in the bed above the filler cap.Since then I've replaced the bed floor with aluminum,and put a trap door above the filler.
Every cell I've seen mounted in the bed ends up collapsing.Mine hasn't changed shape yet.