If you get a Dog Hammock - it's essentially a cover that connects to the front headrests and rear headrests, creating a hammock like space for the dogs while protecting the seats - it should essentially cover up the real tunnel while also protecting the interior, that should work well. If your dogs are big they may have a bit of trouble getting in with the low roofline/smaller door openings.
I have a CLS, which is similar, although I have the 3rd gen which removed the center tunnel for a 5th seat. I use the hammock for my dogs (2 shelties) and they have no trouble getting in and out.
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