at the sound co. i worked at we fashioned plywood pyramids to put on top of our subs so that they wouldn't be drink magnets. we found you didn't need much slope. drunk people value their alcohol and won't put their drink on a surface that is slanted for fear their 5 dollar drink will spill.
worked like a champ. in hindsight, a simple teepee shape that folded back flat on itself with a hinge would have been better for transport. but trust me, put a slant on it and the drink issue will pretty much go away...
brian