[Johnno]

Old hands probably know this already but here is a tip for the less experienced.

Most manufacturers use self tapping screws to fix the body to the chassis, repeated undoing and replacing them can eventually destroy the thread in the plastic because they try to cut a new one each time. Use the following method to avoid damage when reassembling your cars:
Insert screw and turn slowly anticlockwise until you hear and/or feel a click. It is now lined up with the start point of the original thread and can be tightened safely.

It is also a good idea to replace the stock screws with ones like these LINK or longer ones like these LINK. They have a thread-less shoulder at the top which helps achieve good body rock.

This is an old trick that I learnt 25 odd years ago from my old man rebuilding motors, it applies to every single threaded item in the world.

If you do this every single time, you will extend the life of the screw mount and the threaded item for decades, if you feel any kind of resistance, stop immediately and check the threaded hole for crap or blockages, get your air compressor out and blow the hole out and clean the screw/bolt. If you don't have an air compressor pop down to the local service station to put air in your car tyres and use that to blow out the threaded hole, or get the vacuum cleaner out and suck the crap out, if the misses looks surprised just grin and move along, do the job and pack the vacuum cleaner away, she will winder how you vacuumed the house so bloody quickly, again just grin and move on, curiosity will get the better of her eventually