The lid is on and gas struts mounted.
I flipped the original piano hinge upside down so that the protrusion faces downwards, instead of into the mattress. Also replaced all hardware with much better screws.
My drawer unit ended up being 3-4 millimetres higher than it should have, so I cut a very thin piece of wood to place under the back side of the hinge, so that the hinge is level. This raised the hinge up and somewhat exposed the sharp corners. To ensure they don't dig into the mattress, I cut and placed a piece of rubber around the back side of the hinge...
... and then put some wide tape overtop. This should keep all hardware away from the mattress.
I used some of Winnebago's original plastic trim to make these corner caps, and glued them in place.
All done!