I am modeling some packaging that needs to be vacuum formed. I thought the easiest way would be to model the inner surface using surfaces, then knit it all together and thicken. My plan is not working clearly. I know the “thicken surface” function just makes a surface normal to the original that is offset. This works for some curved areas when I knit them individually but does not work when I try and run the operation on small areas that have a lot of curved surfaces.

How would one thicken areas like this?