Dear Skinny,
By far the most damage done to Mini floor pans is from incorrect jacking. Due to the Mini's monocoque structure, few points of the body are strong enough to support the car's weight. The only places you should use a jack are the side jacking points under the doors, under the front subframe where the lower control arm mounts, and under the front end of rear subframe side members. Never ever place the jack under the sump - Not only can you crack the casing but you can also break the engine mounts. Also don't lift the car by the sub frame cross members as they will bend and affect your wheel alignment. And remember to use a set of body stands if your going to crawl under the car.
