Worked on the t'ailer a bit. I finalized the attachment of the diffuser section, and scored the coroplast between the flutes to allow it to curve up around the lower aft bulkhead. I had a roll of aluminum flashing laying around (the stuff MetroMPG mentioned earlier), so I cut a piece of that for an exhaust deflector. It's not real pretty, but it's underneath and out of sight. I guess it turned out OK considering I shaped it with my bare hands, the edge of the workbench, and a framing hammer!
The rear bulkhead was a bit floppy, so I screwed on a frame of aluminum angle to hold it flat. This will be the outer edge of the access opening.
It doesn't LOOK like much progress, but it's necessary stuff that is easier to do now with full access. Once the sides go on, access to some areas will be more difficult.