Thank you very much for the comments, Doug.
I have a couple of ways to go for making the various bows, and I haven't really decided which way I'm going to go yet.
In this shot you can see that the front wall will be framed in 2X4 fir. Here I'll most likely make a template and cut pieces of 2X4 fir and join them with pocket hole screws, then trim the whole thing down to match the curve of the template with the router.
In about the center of that shot you can see an interior bow, a framing bow, and an exterior bow that look to be sandwiched together. Actually, there's a space between the interior bow and the framing bow for the ceiling panel, and a space between the framing bow and the exterior bow for the roof panel. I'll most likely use the same method you used on your canoe to make the interior and exterior bows.
The interior bows are primarily decorative, and we don't really know what species of wood we're going to use there yet. In the drawing I've textured them Red Oak just so I can tell them apart from the framing at a glance. I think I can use 1/4 inch thick strips of material to laminate them together since they're so long. I'll try the bend dry first to see if 1/4 inch thick strips are thin enough to make the bend. If not, I'll have to go with 1/8 inch thick strips.
Here's a screen shot of the interior, looking at the bed. It'll give you an idea of what it'll look like.
The ceiling is "painted" white, but Sketch Up likes to add shadows, so... I've added window trim that matches the interior bows, and built a shelf above the window (no railing on the shelf yet - I'm still designing in my head.) We're debating small shelves or sconce lights flanking the window. I'll also add "stringers" along the sides, running from front to rear, to allow us to hang items from them. I'm debating on running decorative "framing" members along the peak of the roof, between the bows. I think it needs it to finish the design, but DW is undecided at the moment.
I'll use the same method for the exterior bows. They're also primarily decorative, but will also cover the joints in the aluminum roof panels, providing another layer of leak protection. These bows will be painted, and I'm thinking I'll use poplar to make them. Poplar has the strength I'll need, but is relatively light weight for a hard wood.
Here's a screen shot of the exterior bows in place over the aluminum roof panels.
This pic is a little misleading in that it looks like the exterior bows stop at the top of the exterior wall, and a separate piece runs down the wall. I just need to clean up the drawing a bit - Sketch Up added a line at that point for some reason. The horizontal trim pieces running between the exterior bows will have a bevel cut into the top to allow rain water to run off of them, away from the aluminum roof panels, rather than pool on top of them.
Those with sharp eyes will see that the frame has been "painted" to match the exterior body color. DW decided that she didn't like the contrasting black frame. I'm debating on whether or not to run the exterior sheathing on the lower body down further to cover the frame entirely on the sides. She did, however, decide that she liked the black fenders, so we'll use them.