I live close to the show and attended the Model Engineering event a couple of weeks ago. Since then it's hardly stopped raining. The car park is grass with hard roadways.
Parking spaces were boggy at the ME event and a few people had to be towed out. I would guess that the same will be the case at the boat show. It would pay to bring a bit of carpet to aid traction and remember that when the wheels spin, pushing the right foot down harder is not the solution. There were a few lead footed people who struggled before. Better still, bring a few friends who can push if there is a problem. If you have a rear-wheel drive car, load the boot with purchases (sorry dear, I needed the weight to get off the grass) to help!
At least the hard roadways mean once you get moving, exiting the car park is easy. Being prepared is sensible though.
Phil