[Varn]

The foam is going to be the mold. It is going to be a wet layup. Will spray glue on the foam then stick the fabric on.

Paint on epoxy. cover it with peel ply. Remove the peel ply after it cures. It makes a nice surface to apply a secondary bond. The filler can be made from a paste of wood fiber or micro. I will smooth it out similar to what I did on the first section then pry off the parts from the car and get rid of the foam. The part can be then glued or riveted back on to the car. I have built other objects this way including a recumbent bicycle.

Sorry for the long answer.

I still have my original whale tail I may stick it on over this structure. Before I cover it with carbon.

I drove the car into town with tufts on the back tail this evening. My wife verified that the back half of the tail had the straight back flow. The front half of the wing was still turbulent.

Thanks to all who offered ideas so far.