No idea,
But I had considered putting down some saran wrap or some thin sticky plastic, then have spray in bed liner applied to that, trim it and remove the plastic, and you have perfectly fitting molded floor mat.
Just an idea, as I have not tried it.
Also want to think about trapping water between it and the floor. And if you use any sound deadening or insulation first how would that work?

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-