Soft Luggage option
Firstly I have a TTR250 and mulled over this same question until I discovered Kreiger
luggage. I have the 20L main bag and 2 x 10l bags that strap onto the main bag behind the seat. Very watertight, very secure on the bike. I don't need a rack. I also use a small back pack and bum-bag (tools). I've strapped the tyre levers on the bars and have a small puncture repair kit on the front fender. If you pack light it's all you really need.
I carry the following gear:
Small gas stove etc
All of the above I got at a specialist camping store so it is all light weight and packs small.