There's only two bathhouses in San Diego and neither one is that great. The Vulcan is located in the little Italy area close to downtown. The crowd is a little on the older side which can be fun but it's a rather old bathhouse and it's a little too "bright" for my taste. It would be nice if they dimmed down the lights. The other bathhouse is Club San Diego. It's right in the middle of the gay neighborhood of Hillcrest. It's got a slightly younger clientele and it's more fun that Vulcan I would say.
By the way if you're staying near the convention center downtown it generally is farther than most guys are willing to travel. It's downtown and there is no gay area downtown so the general gay population doesn't really go there. Plus parking alone is a bitch. Either way I'm sure you'll have fun Take care