A Kitfox pilot reported loss of aircraft control during landing roll resulting in a runway excursion and landing gear collapse.

Narrative

I had just landed on Runway 24 and was slowing to exit off of the runway. The aircraft made an uncontrolled turn to the south and departed the runway onto the grass. Once on the grass; the passenger side main landing gear collapsed underneath the fuselage. As the gear came up; it caused the pilot side main gear to collapse outward. The reported winds; later verified with airport operations; were 180 degrees at four knots. However; the winds were coming from the side of the airport where buildings are relatively close to the runway. I believe the cause of the uncontrolled turn was a gust of wind that hit the aircraft as a quartering tailwind. The aircraft's tail was on the ground and the elevator was in the full up position. The wind got under the tail and twisted the aircraft. This caused the aircraft to depart the runway onto the grass. There was enough of a side load on the passenger side main landing gear to make it collapse once it stuck in the soft grass surface. It is difficult to determine what could be done to not have this happen again unless you choose not to fly with any type of crosswind. The reported winds were well within the aircraft crosswind limitations but the gust was not. There was no report of gusts in the AWOS. Additional experience flying out of this airport could have provided knowledge about how the winds REALLY feel coming out of the south.