We just replaced the lower windlace on my 50 3100 yesterday. Extreme sound and heat barrier was put down on the cab back, roof and floor. A new rubber floor mat was then placed. The mat could go under the retainer, barrier material and windlace and still get the retainer screwed down. I elected to trim the mat even with the retainer's inside edge, as I wanted to be able to check my brake master cylinder and battery access panel and not have to loosen/ remove the retainer. Other than that fact, I liked the look better with the mat under the retainer.
