Thanks Bowwave. Yes, I've got them.
Got the vacu forming going today - with mixed results at first.
After carefully watching a couple of styrene sheets sagging in the oven and then dropping all the way to the bottom, I was ready for my first go.
As you can see, I got web all over the place
I reasoned that the webbing was caused by too much stretch, so I made a new test and removed the styrene from the oven a little earlier, ie. less sag, but no matter what I did, I couldn't completely avoid webbing
After an hour of soul searching, I thought of the possibility of avoiding the webbing by elevating the moulds. So I made a 10mm elevation and flaired this elevation at the same time - and tried again
And the result was surprisingly good - no webbing and good details
So, tomorrow is dedicated a "series production" of fittings normally difficult to construct in a traditional way.