After relocating the rectifier on a Classic, I mounted a large tool pouch to the stock reg/rec bracket to fill the open space. On the right side to cover the open area left by removal of the Goats Belly make a skirt.
To hang a storage pouch: Make a 3 sided frame (Frame Plans Here) from 3/4in wide 16ga steel that mounts on the inside of the bag...then that bolts to the bracket which also hides the open space not covered by the bag. (Bracket Cover Plans Here) Be sure not to interfere with the side stand. And make sure it is out away from the drive shaft enough to clear it.
To cover the "Goat Gap" on the right side of the bike: Make a 'skirt' (Plans Here) from 16ga steel that bolts to two drilled/tapped holes in the bottom of the swing arm. Make sure it clears the rear part of the frame...since it moves with the swing arm. Paint to match.
Additional Tip: When I paint parts with a spray can...I put them in an electric oven @ 300* for 30 minutes. Makes the paint nice and hard and chip resistant.
NOTE: I purchased a teardrop chrome toolbox from the local Harley dealer and installed it in the bare spot on the left hand side. I bought the RIGHT HAND box. I used the bracket which originally held the rectifier. I drilled out the spot welds on the "U" bracket, and drilled an additional hole in the toolbox to fit the two holes in the bracket which originally held the rectifier/regulator. You can buy a kit from Sherms which includes the necessary brackets for installation if you are so inclined. The Harley kit cost $87.00 but you have to improvise your bracket. The Sherm's version with the bracket is about $105.00.