Not sure if Jason Capley is on here, but when I mentioned on the Facebook VN forum some time back my back issues he posted this workout and it has been amazing. I've returned to routinely riding 4+ hours with no back issues and I am quantifiably faster as a result.
FWIW - I have had back issues since I was 17 when I had meningitis and had multiple spinal taps which left my lower spine wrapped in scar tissue. Through gym work and massage I broke up the scar tissue over the curse of a decade, but it has been tough to get and keep strength and flexibility which obviously are key to performing on the bike for extended periods.
I'm not normally such a salesman, but this really works.