I'm headed off for a 6 day road trip in a few weeks. I am looking for a good sized sissy bar bag like a t-bag or a back seat bag like the t-bags raven. 2 things, I have a detachable backrest but only a solo seat. The pictures I see online all show the bikes with a passenger seat. The other thing I'd like is to use the bag as a backrest at some points during the ride. Do any of you have any suggestions or experience with any bags like this?