Side washing is a great way to go when playing live. It reduces the battle between the FOH guy that has to pound the room in order to get over the sound of your stage rig. Try taking some low end out just to make sure you don't create a boomy mushy stage sound. Most importantly, side washing allows the FOH guy to properly destroy your great stage turning the bass into a solid wall of boom and indistinguishable mud....which is how it's supposed to be, no? A little humor without formally bashing the FOH guy!
JimBob has sage advice, can anyone leave a couple things in the truck? Floyd knows exactly what he is talking about. Know your environment before you go in there. You can also google bands that play there, visit their websites in hopes of finding some gig pics that show how others successfully work the room. powermetal has good recommendations, but keyboard players who aren't Keith Emerson or Jan Hammer just annoy the crud out of me when they try to be hip and "rock out" with the front line. Keytars are cool, but you could be opening a Pandora's Box. I also remember when I thought the backline was a part of the "image". To me and other musicians, yeah we like to see walls of gear...we start sportin' wood almost immediately. But really, the paying customer just wants to hear a great sound and see a fun to watch band. I still play a big rig when I play rock (2-1x15's and 2-4x10's and two racks). But I side wash it so they don't see it anyway. My guitarists for the past 20 years have been also side washing. It really helps the entire front line to hear the instruments, the drummer gets it as well. Win-win. Granted I haven't been playing metal/hard rock as a bassist for a couple years, but back in my AIC, Priest, Scorps, Slayer days....yeah I started that way, but realized I wanted to hear things from the other side of the stage without getting the guitarist in my wedge, and side wash was the ticket. So for me, my image was in my hands and my voice. What the stage looks like means little to anyone who isn't a musician in the grand scope of life. I've had a couple of bands that put chain link fencing and stage drops in front of the back line and I've even told people.."nah, our amps are behind the backdrop so we have more stage room. Nobody but another musician would ever give you any crap about it. And please understand, I don't have an issue with back line being part of the image, but if the gear don't fit, you must acquit. If I only have 2-3 feet of space behind me on stage, I'd be moving my rig, to give me more room to be visual. But again, no offense meant, I just think if you had to side wash to get everyone plenty of room on stage you'll be all the better off. If you have the room on stage, go for it. Not hurting anyone.
Now that all said, bottom line is this, get done...get paid....get booked back......get out. As long as you minimize the discussions about how this is going to "suck", you will be allowed to accomplish your goal of entertaining. Always put the customer first. Do what you have to do, smile, and never let them see you "sweat" the BS of the venue. But the best answer here for you is listen to what BertBass is saying. Just use the stage for drums, keys and back line (if you can't bring yourself to side wash), set your front line up on the floor in front, suck it up and go kick butt with your music.