that's too big I'm afraid. I think my horse must have a very short back as even 6ft rugs are a bit long on him. One with a neck cover is fine though as both his stable and T/O rugs have necks.
What about one of the liners designed to be used with the Rambo Duo? (Can't see why you couldn't use it with another rug, although it has 'trigger clips' at the back to attatch it to the Rambo outer!)
Have just bought LBO the l/w liner for his Duo - it is only 100g, velcro fastenings & light as a feather! Think it cost about 27 quid!