There's just no way you could have a 20x30 traditional awining. It's just too much surface area. An awning that large would have to sit nearly flat, if it did rain, you'd have serious drainage problems. Wind would be a bigger issue. When it's raining, it's often windy. Even my small and wing needs to come in when there's mild wind, an awning that size would need to come in with even an decent breeze.
A tent next to the rig would be much easier.
http://www.amazon.com/gp/aw/d/B009XB15BA?pc_redir=1403803809&robot_redir=1
Something like that would be a much easier option, and probably less expensive in the end. You could but that tent right against the rig and would work just fine. Yes you might get some water run off, but you'd still have weather protection.