I'd try Blender. It doesn't have as cad-like functionality as Fusion, but I'd say that it's better than sketchup. I've been using it for my videogames that i'm making. I heard that there is a cad plugin and a paper model plugin which might be useful.
Fusion's not that hard if you only need to learn how to do stuff related to designing planes. i could learn it all in one afternoon. (not actually all of it, I by no means consider myself knowledgeable in Fusion, as this is only my second time. (it could just be my experience with Blender, though))