Hi Rob, that certainly looks a biggie on the boat Johno's.
I think one reason why the hinges are holding is that I have the bolt at the back of the lid as shown in the pic below so the hinges should not be taking much load. While the hinges provide some support, I would not trust them alone to keep the lid in place. The other thing is that the lid sits in a recess so the edge of the anchor well is keeping the lid from moving too far. I think that so long as I keep the lid secured down then it will be fine.
And I always tie off when anchored on the cleat on the main body of the boat, not on the lid, since the biggest forces would happen when at anchor such as a big storm coming through.