Basically you are right Jon, the weathering powders can and will wear off with prolonged handling.
We use Testors Dullcote as it's a really good quality matt varnish that seems to be quite sympathetic to the weathering and detail. I have tried other more heavy duty spray varnishes but I haven't had a lot of success with these to be honest. I hear good things about other brands such as Valejo but haven't tried them so I can't comment.
As for the UV aspect, I don't personally see it as a problem to be honest. My thinking is quite simple: I don't want to be out in the rain or worse, so I have no need run our finely detailed stock and locos in those conditions either! Dullcote and other varnishes like it are not weather proof, waterproof, splash proof, UV proof or even heavy handling proof. They are a thin and gentle protection for decals and light details from careful handling in an indoor environment, so you really cannot expect anything more. If I do find over the years that some of the weathering powder has worn a bit think in places, a quick dust over the bare spot will more than suffice to restore it back to its former glory!
We try not to handle over stock a lot due to the fine level of detail so I can understand that what I'm suggesting here won't be suitable to everyone. I do think however that for a lot of people, most of their stock stays indoors or in a shed, and as such is rarely run under poor weather conditions anyway, so I would recommend a good quality brand like Dullcote and just be prepared treat your models with a wee bit of TLC.
We use Testors Dullcote as it's a really good quality matt varnish that seems to be quite sympathetic to the weathering and detail. I have tried other more heavy duty spray varnishes but I haven't had a lot of success with these to be honest. I hear good things about other brands such as Valejo but haven't tried them so I can't comment.
As for the UV aspect, I don't personally see it as a problem to be honest. My thinking is quite simple: I don't want to be out in the rain or worse, so I have no need run our finely detailed stock and locos in those conditions either! Dullcote and other varnishes like it are not weather proof, waterproof, splash proof, UV proof or even heavy handling proof. They are a thin and gentle protection for decals and light details from careful handling in an indoor environment, so you really cannot expect anything more. If I do find over the years that some of the weathering powder has worn a bit think in places, a quick dust over the bare spot will more than suffice to restore it back to its former glory!
We try not to handle over stock a lot due to the fine level of detail so I can understand that what I'm suggesting here won't be suitable to everyone. I do think however that for a lot of people, most of their stock stays indoors or in a shed, and as such is rarely run under poor weather conditions anyway, so I would recommend a good quality brand like Dullcote and just be prepared treat your models with a wee bit of TLC.