Need help prepping a place for show


Hi I am going to be playing a show at an upscale car / garage and lounge in LA he wants me to set-up in the garage itself (I'm going to be playing dubstep - hold your jokes)

I need to know a good / cost effective way to make the room sound its best

its pretty much just 4 walls, concrete floor that is coated in some sort of scuff resistant material, roof has a slight arch to it.

I'm afraid that its just going to sound like a bathtub and I need some good ideas to help make sure the sound stays direct and doesn't become a complete wash.

Thanks in advance
Since no one has commented, I can suggest this:

Head down to your local fabric store, buy a bolt of felt fabric (Black is a good color), make a number of 6 ft by 6ft squares of the fabric (or use the bolt width as the square size), and somehow pin them against the walls.

I have my studio in a loft that is concrete, it's the cheapest and best looking way I can get the sound under control.