Since Zero's "Classic Soft Luggage" (specifically the tail bag) is so soft, the tension on the straps varies, depending on how full the bag is. One day I took off for a short ride with the tail bag empty - and the thing fell off.
To remedy this I placed a piece of plastic (about 1 cm thick) inside the bottom of the bag (required some cutting/sewing - I used nylon thread).
Then I also tacked-on a few layers of some non-skid rug backing for cushion and grip.
Then I spray painted this backing with some automotive "bumper" spray (it's supposed to be flexible).
Now I shouldn't have to worry about it falling off again
