Rain cover with ventilation for tono in Mongolian Ger?

[awong]

Hi everyone! I'm purchased a 20' used traditional Mongolian Ger recently and am trying to set it up as a playspace in my backyard in Seattle. We're going to enter the rainy season soon so was wondering if anyone had recommendations on how to keep the rain out of the Tono while also preserving some ventilation.

We're going to add a layer of Tyvek Homewrap under the canvas on the sides and roof. Between the Canvas an the Tyvek, we're hoping this keeps most of the rain out. And we'll be running space heaters on the inside. But I'm just not sure what to do with the Tono. The previous owners gave us a large square piece of plastic. While this will work, I'm worried it'll make the ger really stuffy.

Any cleaver solutions?