This is where I have got to...
I purchased an Ocean South MA501-0 cover as I was keen to ensure that it not only went over the rear frame but also covered the tubes. See
for dimensions etc.
I needed to protect the cover from the fishing rod holders on the frame. I therefore used a piece of 80mm rain water pipe (downpipe) and cut holes in this so that it fits horizontally over the rod holders. From this I have taken another length of downpipe forward, resting on top of the handrail on the console and further forward with a couple of angles so that it ends on top of the anchor locker. Overall looking from above this all looks T shape. Nice and light to lift and remove and it adds some shape to the cover limiting the sagging.
We've had plenty of rain and wind in the past 2 days to test this. Seems ok, with no pooling although I may add a couple of poles angled to the deck from the side of the console to add further form below the cover. I'm also going to use ropes instead of the straps provided as I think they'll be quicker to use and I'll also be able to get them tighter and remove some of the sags.
The cover is really a little long, but I have folders it to cover the complete outboard which I'm happy with. The shape at the front means the electric winch is also covered.