Yakima Bigstack

Has anyone had experience with a Yakima Bigstack?  I picked one up based on reviews but when I tried it out I was getting some pretty bad deflection in the side of my kayak over the rack bars.  It was hot that day but the kayak had only been in the sun long enough to strap it down.  My kayak is a feel free lure 10 which has a rather large flat side (I store it on it's side in the garage).  Car is a Subaru Outback with factory rails.  The kids play boat on the other side had no issues. I'm thinking either I was doing it wrong or i need a larger bearing surface to rest the kayak on.  It travels fine normally on the foam pads with straps.  I ended up strapping the kids boat to the top of mine and diving that way. No issues, but I want to get another kayak.  Am I relegated to the land of trailers?  I like being able to store everything on the wall in the garage at the end of the trip.