Mizzen mast as a ridge pole is an interesting idea that I hadn't considered. My first thought is that it would be too much for set-up and tear down having to deal with the mast, sail, sprit, downhaul, snotter, etc.
My current setup (CS17) is like a boom tent but just using a line instead of a rigid peak. The line hooks low on the main mast and rises to the snotter eye on the mizzen mast. PVC conduit stiffens the trailing edge against the mizzen mast. (Picture attached (I think)).
I've spent a couple of rainy nights with this setup and it works better than I expected. Setup is probably less than half of the time it takes me to setup my land tend. I do carry a simple bivy sack in case I need more rain/wind protection.
I am debating on whether to improve on this design or proceed with the dodger/soft cabin idea that I have been mulling over for a while. It would be good to have something to extend aft of the mizzen mast because my head tends to lie on the center thwart.