Japanese System Kitchen - I've hit a wall...

I have been working on the system kitchen, but I've been having some difficulty. The sink. I want the counter and sink to look like one piece of molded metal. The counter came out to my satisfaction, but the sink has not.

I built the thing out of wood and thought my typical gesso-sand-repeat routine would get it smooth enough for spray painting. That's the same thing I did with the counter, so it should've worked. Well, it didn't. I can't get to the tiny curves to sand smooth. I don't want ridges, so this is absolutely unacceptable. I tried a jelly container initially, but they must be making them with really crappy plastic now because the plastic kind of melted with spray painting. (I have used the jelly containers in the past even spray painting them, and it worked well.)

See those awful interior joints? I want smooooooth.

The only thing I've been able to come up with is looking for someone to actually mold the little sink for me in plastic or metal. It would still need to be painted to match the counter. Maybe I just need to look into resin casting...?

If anyone out there has the inclination to post a suggestion, I would greatly welcome it.