Hi Graham, don't worry you're not being a pain, you're just learning how to use the software! Helping people with problem areas tends to help me understand what things need to be improved in future versions to make things easier.

In this case you've still got a mis-matched endpoint problem on the inside loop. Check out the image from my previous message again - there are actually 2 areas that needed to be tuned up, the second area is also circled in red sort of in the lower right-hand area.

Your new model has fixed the first problem in the outer loop, but not the equivalent second problem in the inner loop. Once you fix the endpoints of the inner loop to align, then you can extrude everything and get the clear inside like you want. Let me know if you still have problems with this and I will give you some clearer steps.

By the way, your illustration in the center looks nice and clear, it will be cool to see this finished!

- Michael