I wouldn't use solid top box on any of the R11xxGSes if you go travelling into the third world's potholed/corrugated roads - it just vibrates and shakes as hell puting all that shaky stress on the subframe that's already stressed with a lot of weight from your side boxes. Unless you want to use the bike only for communiting and city riding on Western-Europe smooth roads.
They are prone to break the rear frame when heavily loaded and ridden on bad roads. I've seen too many GSes with broken subframes mainly because of the overloaded solid top boxes. Whether they break the carrier frame (the silver one made of "chocolate" poor quality metal) or the tubular subframe close to the engine mountings.
Cheap waterproof luggage roll is the way to go IMHO. Weights less, carries more, keeps the weight more low and it's self-suspensioned - less stress to subframe even with higher loads when riding bad roads. You can take the roll off in 5 seconds, mount it back in 15 sec with 2-straps and it's easy to carry to hotel etc with it's hook where you can grab it. Very easy to use when you get used with them (and that's coming from an ex-topbox convenience fan).