Welcome LizzieB.
You will love your Triton and have loads of fun with it. Frantone is right you can leave your top up even if it rains really heavy, although it is a good idea to fasten the zips up in your vents if it rains really hard at an angle to the van.
There has been lots of debate on the Forum about putting the pop top down in freezing weather to keep the temperature inside the van up. I'm one who keeps the top up if I can. We've never done snow yet so can't advise on that but guess you would put it down so the weight does not damage the roof hinges.
Good luck in Norfolk MikeT