Ok, I have an update for you all...
I started working on the chest lid. I began by making a 1 1/4" high base for the lid. I carefully made sure that it matched the top of the chest base and squared it off with triangular blocks in the corners to add stability
Then I carved the lid sides and glued them in place...
I carved the lid slats (4 of them, 2 sides and two thin ones for the top) and laid them in place. You can see spaces between the slats as I haven't glued them in place yet. Also, I have push pins holding the side panals in place on the base while glue dries so the slats can't lay flush until I remove the pins. I was just checking for their fit and so far, so good.
I've decided on a paint color (It'll match the base of our animated Deadeye Drake). I'll have Lowes match the color in a good exterior latex (same as I use for my tombstones, it's worth the expense). I'll then take a black sharpie to the woodgrain groves and knots...a little drybrushing over it all and that should work for the paint. By the way, I also carved the wood grain on the inside of the lid as well.
Hubby and I were thinking of buying real wroght iron hardware for corner brackets (they're fairly cheap) and I'm going to line the inside of the chest with felt...well, that's the plan at this stage
We're still working out how to hinge the lid as polystyrene is weak. I'm considering a piano hinge set in place with wood screws steeped in Elmer's wood glue. A piano hinge would run the length of the inside back of the chest and be covered by the felt. I'm not sure yet about it though.
ETA: I forgot to mention that I'm planning on making vertical straps for the chest out of Crayola Model Magic Clay (fantastic stuff if you haven't checked it out yet) and paint them black. We'll also adorn the chest straps with brass capped tacks.