I had a magnetic tankbag, but didn't use it much since taking it on and off at fill ups without scratching the tank was tedious. Eventually it just started to scratch the tank anyway. So I just picked up a Givi xs308 which mounts to a tankring, so no contact on the paint, it goes on and off super easy. I run it on the bike all the time, it never comes off.
2009 Wee Strom ABS (current)
1987 Harley Low Rider Sport (current - with 205K miles)
2009 Aprilia Mana 850, 2006 SV650, 1984 Yamaha Virago 1000 (all sold)
Silver Strom Club Member #11
Wee Farkles: Russell Day Long Seat, Madstad with Moose Adventure Shield +4'', SWMotech Centerstand, 1'' up & back bar risers, Givi XS308 Tankbag, Aprilia mirrors, Framesliders, Fenda Extenda, Elka Shock.