Yes, you could use these velcro straps to secure a trunk bag. They are normally used to secure the bag to the upturned part of the front of the rack to prevent the bag from sliding back. I screwed in an 'L' bracket to the back of my rack to keep the bag from sliding backwards and now i'm able to use these velcro straps for whatever. Unfortunately, on my bag, the two hooks that hook to the rack on the bottom broke off. With my rack, when i'd hook into the bottom, the hooks weren't really that tight and would often come out. Well this happened a couple of times and usually the strap on the bag would hold the hook back but a couple of times the hooks got free and as they dangled around they caught a spoke and ripped off my bag. So now both hooks are gone and i basically just have the bag laying over my rack - so i have to now use the velcro straps to secure it. This works ok but when i'm pumping hard and stuff the bag will flop around from side to side which is kind of annoying. I tried putting a small carabiner in the strap on the bag and hooking that around the bottom of my rack, but it's too loose and makes a racket. I was thinking of putting a loop of innertube around that strap and using this to connect to my rack but i'm open to any other ideas you guys may have. I still really like the bag though and would only hesitate to recommend it because of the hooks.