My Koni FSD's are still good after two years and almost 25,000 miles on my Airstream Avenue (think 190P and you've got an idea of my model.)
They do ride well, control secondary motions, and side winds. But then, I was replacing worn out OEM shocks so anything would have been an improvement. I specifically ordered the FSD's because the were NOT gas-charged, thinking this would soften the initial impact of road imperfections. They were also the priciest out there and I decided to see if spending more money bought me anything.
When the Koni's arrived and I took them out of the box, I could easily compress and expand them. I was used to gas-charged shocks you could not budge and so I was sure I'd made a huge mistake and there was no way they could control a 9000+ lb van. But, they do a great job. I would go with them again, especially if Koni stands behind their warranty (I'll be checking for leaks).
Just my limited experience. Can't imagine changing shocks annually. Hope your set up lasts a lot longer this time.