I'm not an M3W person but I will make one observation if I may, it being that Calum he of lovely pictures, many miles and Portugal Hill Climb fame got caught out in the wet on a busy Scottish highway when the rear wheel let go and he was a passenger after that fortunately he was uninjured but the car was a rebuild job.
I agree, the main concern to me when driving in heavy rain is rear wheel aquaplaning. It's hard to explain unless you've experienced it but basically you are just a passenger when it occurs. A newish rear tyre with good water shifting properties will help but not eliminate the problem.
Having said that, my first trip in my 2012 car was 170 miles from the New Forest (where the seller lived) to my home in Leicestershire. It did stay dry and I had Mrs Bunny in a support car but in the event it was a trouble-free trip.
