Here is a nylon (Shapeways) frame on top with an Atlas B23-7 fuel tank and reservoirs part snapped in place. A revised version of the frame is below. The revised frame is used with a laser-cut steel frame part to give the assembly a bit of weight but more importantly rigidity and strength.

A 3D printed fuel and reservoirs have been added to the revised frame. A comparison between the Atlas parts and the printed parts shows the difference in width and diameter of the reservoirs as well as the width of the base of the fuel tank.