I had another go tonight. I set my scope up at 6.00 pm and was onto Jupiter very quickly. The first thing I did was make sure I was definitely saving files. I then had a look in the camera configuration and was able to turn the gain down to the point where I could begin to see detail on the planet, although at the expense of no longer being able to see the moons. I took many similar looking frames over the next hour, while clouds rolled in and away. This is one of the frames; I've cropped it and adjusted the brightness slightly but otherwise this is as it arrived on my laptop. There are some tools for stacking frames but I've yet to dig into that.
At 6.45 there was a very bright ISS pass - it came tantalisingly close to Jupiter, but well outside the field of the view of my scope. Not long after I ran out of battery power for the scope's RA drive - not bad given that I don't think I've ever changed the batteries.
So there you go - Jupiter, from my back garden. Pretty pleased with that.