Here is a simple Confer dual battery box. A bit big for 2 Optimas, fitting it into your cruiser could be intersting.

Here is a custom Butch Built dual optima battery box. Very well-designed and well-fit into the cruiser. There is no comparision betwen this tray and the Confer box. You get what you pay for. Btw, it fits into the original mounting bracket used for the OEM battery tray, the tray even clears the alternator in case a York air compressor is installed. The only minor modification
is the moving of the stock coil bracket forward to the front on the fender which can be done easily.