Why won't surface model fill in?

Here is a part I'm working on for a client, some sort of equipment cover. I originally made the part in regular solid modeling, but was unable to shell the model with all the intersecting fillets.

SOOOOO... I tried surfacing, which I have zero experience with (it's been a fun week). After the initial outer surfaces were completed I tried to thicken, but was unsuccessful, so I resorted to offsetting inward and closing the shell. This necessitated several delete and fill operations followed by knitting all the faces together.
On the last knit operation (Surface-Knit 38) I selected Create Solid, and the operation completed without throwing any errors.

BUT... the part is not solid, it's still two offset surfaces.

There's one seam inside (look just past the end of the yellow face underneath, it's small) that I cannot knit together, but I'm not sure that's the problem.

Any thoughts on why this part won't fill in? (and please go easy, remember I'm a rank noob with surfacing)

Thanks guys!

2 Answers

Quick fix works..............
Still a deplorable model.

Here is the fix I did in SW2020. I rolled back before your Knit38 and did a new Knit and it worked. I then suppressed your last few features and did a keep body of just the solid.