Leaking zip on groundsheet in awning.

Blessed

I bought a drive away awning with a zipped in groundsheet,for my motorhome.

When it rains heavily water pours through the seam above and below zip ( don't think it comes through zip )  filling the inside like a paddling pool.

I've thought of unzipping groundsheet and rolling in at sides, using Seam Seal on double stiching of zip, covering zip on groundsheet with Gorilla Tape or putting a light weight tarpaulin over the whole awning.

Has anyone any suggestions to overcome this problem.

Thank you.