ePanelBuilder
Why not use the e Panel Builder appication on-line? It doesn't cost anything to register, they provide free templates for the various RV panels, and they provide properly sized instruments that you can drag and drop to your heart's content.
Then when you're ready to build your panel, you can pay them a fee (I think it's about $40), and they'll use your design to create an autocad file, and waterjet to cut you panel to your specs.
You can find it by going to WhiskeyVictor.com or epanelbuilder.com.