This is an awesome little addition to help with rear storage in your Rivian. With a strong velcro backing, it'll basically stick any where there's carpet, so in the R1T, the best spot is under the rear seats, as shown in the pictures. Great for storing things like sunglasses, charge cards, etc. Made from high-grade flexible silicone, it's washable if needed, unobtrusive, and has a flap to cover & protect the contents.
Internal dimensions are 7.5" x 3" x 1.3" (195mm x 75 x 33). The front-back dimension can vary a little to expand for larger sunglasses, since it's made from silicone.