Our single backseat extender took weeks to arrive, and when it did, two of the four support rods and the bungee-type tether pictured on the product page were missing. Customer service promptly sent out the tether (another long-ish wait), but we had to hunt down rods from a local hardware store. Without them, the sides will cave in. But even with everything assembled properly, our 30-pound, senior sheltie can still hop over the sides and onto the backseat, so a travel crate will likely be the