Joel mentioned placing carpet remnants.

I did this when I had the other van and they move around quite a bit.

I accidently found some clips that were called Carpet Stays. That did the 
job to keep the units in place.

The stays have aligator-type clips on the top and straight-pins in the 
bottom. The pins are inserted into the existing flooring and the clips are 
attached to the carpet remnants. Works like a charm.

I  have since seen several brand/items that are similar. Even saw somethng 
at K-Mart.

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