Any wind noise or side effects with that size bag?
Will the bag work well with the stock KTM 990 rack or do I need a base?
No wind noise since it is behind you. And the zippers are butter to operate. I can close then one handed when riding in case I forget to do so before taking off (not that I have ever done anything like that. Anybody who says otherwise is lying
On my SMT it just mounts on the stock rack. It has 4 bungee and hooks that can be adjusted in length.
It also has an expandable gusset so if you unzip that you can fit a helmet in it.