Designing A New Gas Tank

I started this in 2008, I know, I'm very slow.  I also lost some pictures.  I think they were on a hard drive which died and some how missed all my backups.
The old fuel tank held 18 gallons which was great for cross country flights.  I don't care about pushing quite that far on a tank of gas so I'm working on a smaller tank to solve the 3 problems with the old tank.
The filler neck of the tank didn't clear the cowling so it sat in a bowl with a drain.  If the drain plugged, as all drains do, water ran in around the gas cap.
The flat bottom on the old tank allowed 16 ounces of water to be in the tank and undetectable on the ground but get into the drain in flight.  It always seems to take more than one problem to cause a disaster.
The flat bottom also limited space for my size 14 feet.  Pete originally designed the plane for a 12 gallon CUB tank, which gave plenty of foot room.  Any capacity over 12 gallons will be great.  My math says it should be 14.38 gallons.

Because of the lost pictures, you'll have to imagine a little.  I took 2 pieces of cardboard and taped a box between them to define the front and back of the tank.  Picture a square spool with 2 wide flat ends.  I put this in the plane with my biggest pair of boots strapped to the rudder pedals.  I then drew the bottom of the tank to clear my boots.  The top was drawn to leave a little clearance between the tank and cowling.  I didn't want much clearance because I wanted the filler neck to stick out properly.
The ends were trimmed to shape and some poster board was taped on to form a pattern for the outer wrap.

The idea was to hang it from some straps like the CUB tank so the bottom had to be parallel to the top longerons on the fuselage.

 The length was limited by the firewall and the need for clearance behind the instruments for connecting all the lines and cables.

You can see how the top tapers to follow the slope of the cowling. The filler neck will be at the aft, highest, end of the tank.

 Here is the finished mock up.  The square holes in the end plate were cut to help tape the ends securely to the box between them.

I decided to reshape the tank sides slightly to increase it's size and to let it rest on some supports on each side of the fuselage.

 The supports were made form 3/4" plywood so they could set on the old tank supports.  These new supports get bolted to the sides with the bolts which hold the straps clamping the tank down.

 The supports set slightly above the longerons so the weight is on the old tank supports, not the upper longerons.

There are some blocks glued on the back which actually set on the old supports and, at the top, hold the block parallel to the fuselage sides.

 The support on the left also made a great place to attach all the engine controls a, wires, etc.

Everything worked out well to be able to continue using our old Army surplus throttle quadrant.