Greg,
I looked at your album. Your trailer design has really developed. Nice work, I really like it.
I play around in Sketchup a little, and also do some personal/business design things in TurboCad, but I'm still a duffer. TurboCad Learning Edition used to be available as freeware on the internet. I couldn't find it ten minutes ago, but maybe it's still out there. That's what I started with several years ago. Now I have TC v9.0, but even that's probably old now. The thing is, TurboCad Learning Edition is really pretty basic and intuitive. If you can do Sketchup, you could work with (not master) TC LE in an hour or two. That way you would have another tool to work with. The v9.0 that I have will let me save drawings in many formats, including .dxf and I suspect that LE might also allow that too. One of the other CAD users might be able to verify that.
I use Turbo cad to think things out in two dimensions. The Sketchup helps me think in three dimensions. From looking at your album drawings I'm sure you could learn the basic CAD functions quickly.
JB