The airline transport pilot was on a Title 14, CFR Part 135, cargo flight when the accident occurred. The pilot reported that during landing, the main wheels were on the ground, and as he lowered the tail, a direct crosswind gust that he estimated to be about 15 knots struck the airplane. He said he attempted to counter the gust with power to the upwind engine, but was unable to counter the effect of the gust, and pulled power from both engines, and applied the brakes. He reported that the airplane went off the runway, and made a 180 degree left turn. During the excursion he said the right main landing gear collapsed. In a written statement the pilot said he should have flown over the field and checked the windsock rather than make a straight-in landing. He said there were no known mechanical problems with the airplane prior to the accident. The right wing of the airplane received substantial damage when the right main landing gear collapsed.