Great work D4D - you'll be happy as a pig in mud.
I think you'll be very happy woth the DPO package - it includes the pull-out storage drawer, doesn't it? Initially I didn't want one. I thought that it would make the camper tub not as useful by breaking it up into smaller fixed sections, etc. Thought they were very expensive for a plywood box. Now however, I'm in the process of building one for our camper because I'm so sick of climbing in to reach the stuff right at the front. So far I'm about $400 into the project, and about half complete. I'd be kidding myself if I thought that I'd be able to finish it to the same level that the Drifta products are. I can't wait to get it done, it's going to make life so much easier at camp.
I'd also go the spare on the back. I've got mine there, and it's perfect. You'll always find more stuff to stick on the drawbar down the track - getting the spare off onto the tailgate just gives you more options. Not sure about other camper's drawbar weights, but I can easily lift mine up. I've got the wheel on the tailgate, and the watertank behind the axle (but my axle is pretty far back too...).
I'd also look into getting the canvas tailgate draft curtain that KB mentioned. It's another thing I'm considering doing to mine. Just a piece of canvas, with press-studs around the outside. If you were fancy you could quilt in a piece of airspan insulation. Once I have my kitchen set up, I don't want to have to unhook gas lines, fold over benches, etc, to pack it up every night.
Did you end up going for the gal chassis?
Sounds like you've got an awesome unit on the way - I can't wait to see the pics of it in the flesh!
Cheers,
Matto