The original poster hasn't been back in nearly a month.
I have a SnugTop canopy. It seals rather well, importantly the sides have a lip that sits over the top of the tub, and a rubber seal that sits over the front between the tub & cabin. Water ingress is mostly prevented - there are a couple of drips present in major downpours that are attributable to the window seals, but the canopy itself is quite good.
I don't know what its loading capacity is. I should probably ask my dealer, because one day I do intend to put a basket up there. Hopefully I'll get more than a pair of snow skis and a Gucci handbag on it. Not that I'm trying to infer anything about BMW drivers heading for Thredbo, no sir, not me.