Touring Equipment

If you really want to go ultralight, and you're considering a trunk bag of that size you'd be better with a bikepacking saddlebag surely...It'll be lighter than a rack and trunk bag and fit more in it.
Or are you also using panniers?

To be honest I'd never looked in to that, but they seem very up to the job the ones from revelate designs actually hold more (L) than the rack pack would anyway.