I got back to building today, but here are some pics that I haven't posted yet.
I added spars to the roof.
After placing a piece of masonite across the spars, I found that they bowed inward a little. Tomorrow, I want to turn the spars vertically. This should take care of the bowing.
Then I started on the wheel wells by building the frame:
To protect the masonite wall, I decided to cover with flashing. I put down some roof coating over the masonite then covered with the aluminum flashing:
Then I folded the aluminum over the edges and tacked it up.