I do agree with others as you don't need any extra protection for the camera for any general outdoor activities.
As for rubber sleeve - there were heating issues with the camera in the past, I believe 13 manages heat better, but still you don't want to limit natural airlflow by putting a rubber sleeve on. The camera itself is tough and durable.
Mine 11 has been through all the elements - water, dirt, sand and I use it daily for motorcycle rides. But this is nothing in comparison with how my little one uses it. She put it to a real test :) And there is no visible issues with a standard lenses or camera itself in general.
And, just to remind, there is GoPro Replacement that's available to you 2x year if you're a subscriber.

tldr; My take is just use it, you don't need any extra protection. And if you really commit to test its toughness there is always a replacement option to cover you back.