Hi, yes, my SprintX has rear suspension. I saw that Fastback bag on eBay but it looked a bit battered to me - but I think mine may well have been a Fastback, it certainly had the same Velcro strips and the pad. Sadly no longer available. The trike has the rigid seat.
I'll have a look at the banana bags, thx.
Just dragged out a 26" and 20" Marathon Plus from the attic that were on my Performer; I went to Marathon Racers and they've been good. Thought I'd try them on the trike as it currently has Kojaks and I live in hawthorn hedge country (rural Cheshire).