I just last night added a narrow seat post rack on my road bike and put a bag on it. I decided to affix it permanently, and so not much point in buying something with mounting brackets, quick releases, and so on. A light bag/pack, coroplast cut and shaped inside it for a semi-aero look, ziptied down and done. The look is more sleek and less bulky and not as boxy, and likely lighter, than retail trunk bags IMO. I could fill the whole bag up if I want and it would still be secure but the 4 or 5 inches height of the sides is mostly enough.


I'll maybe post up some pictures later, but the DIY route is something to consider. I've used the bag for years, basically zero cost, and start to finish took about half an hour, so who cares if it's out in the weather - no reason to remove it.