Oh sweet Jesus, sounds like I'm going to open a right can of worms here

I've not had a really good look under it yet due to the weather and the wobble problems lol

Do you drill out the top rivets?

I've got a bit rust in the sunroof well where the drainage holes are but it's not much at all. I suppose this would mean the drainage holes are slightly blocked or the car has been parked in such a way the water has just laid in the well.