Hi Duke, I've attached a finished up version, which tries to show some steps unfortunately the last clean-up part is a bit detailed and hard to describe shortly, but I'll try...

With these kinds of shapes you tend to have to use the more advanced parts of the toolset with stuff like some "low-level" tools like individual surfacing and surface trimming...

Here is the sequence that I used, except there are several trimming steps for that last stage:



But what I did is start with some of the "high level" solid modeling tools to kind of get a jumpstart.

First of all, let me show you this corner in the finished result:



Notice how the original surface had 1 common vertex on the outside, but this final result has a kind of "diverging vertex" where there are 2 points on the final result with an edge between them - that kind of diverging corner situation is not handled by MoI's Shell tool automatically, it is because of this part of the shape that you can't just do a shell of the whole thing and just be all done. Not with MoI's sheller anyway, there are more advanced shell tools in other NURBS programs that could probably do it though.

So just one simple use of Shell is not going to cut it.

What I did was to build those 3-sided corners with sweeps with the bottom line as the profile curve, and the 2 long upwards edges as rails.

Then I used Edit/Separate to break everything into individual surfaces.

Then I selected all those surfaces, and use Shell to thicken each individual surface into a solid. This does not handle the inter-connections between the pieces all fully properly but it does get quite a few pieces in place. Then I used boolean union on all those pieces to fuse them all together into one solid. You can see that the base part looks all fine but there are some kind of excess corner pieces.

Then I used Edit/Separate to break this into individual surfaces again, deleted those little slivery excess parts in the corners, drew a line across here:



To trim the excess part of that yellow surface there off, then I built a kind of cover sheet over the top using Network with the 4 outside edges:



So then there is kind of a cap on top and it is actually intersecting the inner 4 surfaces, so the top cap and those inner 4 surfaces can all be trimmed to one another. Here I have hidden all the other surfaces and have just the 4 inner surfaces and the top cap visible.



To trim, those all get selected, then run Edit/Trim, right-click at the select cutting objects prompt since all objects will cut each other.

Then you pick which parts to discard or keep. In this case there are some pretty thin pieces of those side-walls to get rid of, the pieces to keep are bigger, so it is easier to switch the mode to Keep and pick the 5 pieces to keep, which looks like this:



Then join all the pieces together, that's how I got that final result.

Hope this helps, like I mentioned to do these kinds of shapes that are not very mechanical you're going to be dealing with a more advanced part of the toolset that is also harder to learn.

- Michael