Here is a picture of the skin trimmed.
An old picture showing where the four spars are. I did add two cross braces (no photo) and braces all the way forward at the bottom of where the skin goes. With the skin on I cut the four spars in between the two skins.
A couple of photos showing the hatch propped open.
A seal has to run down both sides, and 1/8" ply is not wide enough. My solution is to glue more ply on the inside. I added three layers, with each layer just a little further back, so I could sand it parallel to the skin that will be put there.
This process took several days, and many many clamps.
Time for the first side of skin.
Trim to shape. I used an 8' aluminum ruler to find the trim line.
Installed the second side and trimmed.
The latch is installed flush with the top of the counter. Trim so it fits through the braces.
The top piece is 3/4" ply trimmed so the base of the latch sticks through. The latch bolts to this piece of ply.
I added these two pieces of 1 by that are only glued to the spars. I used spacers 5.2mm ply to hold the bottom framework off the body (to leave room for seal). The spars in time will be cut from the body (no it is not time yet)
Another view.
In the space left I added a small triangle of 1/2" ply secured to the 1 by, that a metal striker will mount to. Note the small rectangle piece of ply is a temporary shim. 
When I laid out the sides I marked the door cut out, which should show through the fiberglass. Using a jig saw I cut out the window first, then the door.
Now I need to build a lip for the door to seal on. Andrew made this drawing (thanks Andrew). The purple (maybe it is blue) is the body. I am adding two pieces, an 1/8" spacer, to give room for the seal (black in the illustration) and the lip.
Due to the complex shape, I built the spacer out of many small pieces. Each piece is custom fit and goes all the way back to the interior spar. Cut out the general shape and held it in place and drew the curve, cut out with jig saw, glue and clamp. Do not make more than you can clamp. Let dry overnight, remove clamps and sand for exact shape. I made the lip out of two layers of 5.2mm ply (I have no idea where it came from, but it is nice thin ply). The lip is 3/4". Do not put the seams in the same place. This took about a week of clamping, letting the glue dry, cutting a piece to go over it, gluing, clamping.....
After sanding, coat the entire thing with fiberglass resin.
To put a bottom on the tag box I cut a piece of 1/4 ply wide enough to fit between the braces, and slid it in. Holding it in place I traced the shape of the skin and cut.
I glued it in place, set my clamps to spread , and held it in place.
Added some fiberglass resin to coat the top, and filleted the bottom.
I hid the compartment vent in front of the tag (the battery goes in this compartment). When stapling this panel on I clamped the bottom so it bowed upward (figured the water would flow out).
Once glued and stapled, remove metal and fiberglass.