All the RC planes that I draw, I draw in 3D in Autocad. then I use the Section command to get ribs, formers, etc. Another good thing about Draftsight is I can view all my 3D RC plans in it. Although its slated as a 2D program it still is programmed on a 3D platform. You can make basic 3d shapes with it by using the "3d" Command.
Heres' an Arrow wing I did in Autocad opened up in Draftsight. So Draftsight is based on a 3d platform. You just won't be seeing the neat 3d commands being added to it as afterall it's programmed by the same company as Solidworks and Catia. I can say if you learn it you'll be right at home with any version of Autocad LT (light).
I agree that it's the best way to test fit before you actually have a kit lasercut. The Interference Command in Autocad is an awesome tool for checking the fitment of parts.
I've been slowly learning Solidworks.
I'm glad I learned Autocad as I now get paid for drawing plans for unpermitted additions. Seven sheets including a Title page and notes can drop $1250 in you pocket when someone needs a set of plans to get an after the fact permit.for closing escrow.