Here's kind of a different way that you might approach building a shape that you want to have end up with a thickness to it.

This way uses the Shell tool to create the thickness at the end instead of trying to model the thickness directly along the way.

With this method you focus more on the full exterior shape of the model first.

Just a quick example - here I start with a curve:



Extrude it to get a solid:



Draw a profile curve in the side view which will be used to cut the solid:



Select the solid, then run Construct / Boolean / Difference, and pick the profile curve as the cutting object. This will cut the solid into 2 pieces, and you can delete the top piece, leaving you with this result:





Now to create thickness, select the front and bottom faces (note here the whole object is not selected, I have clicked a second time on it to drill-in and select just 2 faces of the solid instead of the whole thing):



Then you can run the Construct / Offset / Shell command to create a wall thickness:




This way tends to be easier to work with the kind of outside form of the shape first, that way you can carve off pieces with booleans easier and leave the full width of the kind of "imprint" of the carving piece.

If you have modeled a solid that already has a thickness to it, then when you carve off a piece of it from a side profile, it will only leave the "imprint" along the part inside the walls since that is the interior of the solid...

Does that make any sense?


Otherwise the way that you did it initially of building it more directly to the thickness by surfaces at a time would need to continue that route and build more individual surfaces like by the lofting and Planar methods that I showed previously. That's kind of a more "low level" approach building it a piece at a time instead of working on the outer solid initially.

- Michael