I’ve run a GXP crank for a couple of years on one of my bikes and have just replaced it with SLX. That tells you all you need to know.
The more recent GXP BBs have a “Gutter Seal” which is a plastic shim that fills the gaps between the axle splines, so as to prevent water ingress from damaging the bearings from the inside. It probably won’t make much difference though, as I’ve dismantled a couple of ronnied Truvativ BBs and have found that the bearings cosmetcially look fine, so it’s not rust that’s causing the problems in my particular case.
Oh and nine months for a GXP BB used only in dry weather is about the best you can expect. By comparison, I’ve Shimano BBs that are about to enter their third year and which are doing just fine. If you really like your GXP cranks then a Hope BB is the only way to go, otherwise go Shimano.