Thanks guys.
@Drew: These were pretty much straight cut, but posterboard is so thin that it really wouldnt make a difference either way.
@Oscar: I know what ya mean, $20 would buy quite a stack of blue posterboard at Office Depot.
I've seen the site you linked to, and figured without an original to work from it would be easier to add a flange at each corner and staple the pieces together. If you wanted to make it like the Toobin' bezel in one piece you could simply make a pattern in white posterboard and once it fits just open one corner back up and trace the whole thing as one piece. I cut the tube curvature as I made each piece. My measurements showed the tube only varies 1/4" from a corner to the middle, so the curves are pretty simple to lay out and cut.
I can post the plans, but honestly I dunno what use they'd be as I ended up just free hand cutting the bezel to fit. I'll see about "digitizing" the third pattern and will post the results, but you'll still need to play with it as your cab is likely different and my pattern won't fit it as is. I'll also take more pictures of the third pattern tommorow, and attempt to better explain how I went about making it.