Well after a few days of rain I'm officially calling the Meguiar's product a failure, in fact I would say WRT rain resistance that it's significantly worse than Back to Black. It runs badly in the rain, and after 3 raining days in a row, it was completely gone from the cladding. The last coat was super thick and apparently it made no difference. If you live in a place with 300+ days of sunshine (hello Arizona folks) it's really a great product; it leaves a dark satiny finish without the greasy feel of Back to Black, and it stands up to sun very well. But for the rest of us (especially those in the PNW) I think it's a no-go.
On the plus side, since everything had washed off the cladding I decided to do a full coat of 303 to test it out. Good news is that it's supposed to rain for the next 2-3 days, so should be a pretty direct comparison to the Meguiar's. So far it looks great, at least as dark as Back to Black or Meguiar's. No oily finish like B2B, but I haven't run a California Car Duster over it yet. Another review to follow later this week...