I did this, but just went with the gorilla tape myself. Leaked a little, but having expected this, I just kept the hose ready and sprayed what little leaked out.
I've thought about cutting some plastic pieces to seal up the holes if I ever do the acid wash again. Maybe use some O-rings under the plastic bits to get a better seal? Seems like it would be the best route to go in my opinion. (I would plan on using a el-cheapo dollar store cutting board)
I had really good results when I did my tank. Did you do a follow up coat with Navel Jelly after the acid? Supposedly, the Navel Jelly not only cleans the metal further, but the reaction leaves the bare metal more protected and prevents flash rust.
With the muriatic acid by itself, the metal flash rusts very quickly (within minutes)
......I'd rather wake up in the middle of nowhere then in any city on earth.
*2014 VN900 Custom (16,200 miles and counting)