Myles,
There is a backing strip about 1/8 inches wide at the four sheet joints. There will be no internal bracing on this tank. The next tank I am building is 18 inches across. I will have bracing on the roof of that tank to prevent the cone from inverting during shipping. The shell does not require bracing because it is round. If I glued braces on you would see distortions in the styrene at the glue joints.
Alan Graziano