From the start I was determined not to put the sender in the side of the tank. Mine will go on top, recessed. I cut a 5"by 5" opening in the top of the tank. Strengthened the circumerence by adding adding angles...shrunk two of them to match the curve of the tank. Rivet spacing will be 3/4". Notice one additional dimpled hole in each angle...this will be a place holder, with a flush mounted rivet to hold the angles in place. I'm working on the top component which will house the sender. More to come.
