I've done the SPI to Port O'Conner stretch a few times. Given that I don't know the draft of your boat, the only thing that comes to mind that would be safe in that area for most drafts would be Army Hole. you can tie up to the docks there. It's a relatively nice, quiet area. Or, if the waves and winds aren't horrible, you could drop anchor in Espirtu Santos bay. Offatts Bayou by Galveston can be a nice place to drop hook and stay out of the way of the ferry and barges.