Thanks for the links, it's nice to see the ideas and cute pups! I've been considering getting a cheap topcase and modifying it to suit a small dog; right now I've got a Givi that I'm loathe to do anything to, but I've seen some others that run under $30 that wouldn't break my bank. The only problem with a top case is that I'd worry about exhaust getting into the cage. Perhaps only make vent holes on the non-exhaust side?
A tank bag would probably work best, although probably not give as much room as a topcase would. Perhaps some venting on the non-exhaust side, a hole in the top with a magnetic flap that can cover in case of rain etc. Yeah, brainstorming - I want to use my 'Strom as my sole mode of transportation and this includes being able to take my pup to the vet or dog park whenever she or I feel like it.
1981 GL500 Silverwing
2008 Wee-Strom 650 - bright "Look at me!" yellow