Prius rear wiper delete plug Gen 3

I deleted the rear wiper from my 2015 Toyota Prius. I borrowed the original model to open in slicer, cut and resize to my needs. I am new to 3D printing and welcome any design modifications to this plug! I would love a way to better secure it from the inside, like a screw tight method threading the inside of the plug and having a large male screw or nut to tighten. For now, it's just held in with RTV sealant. Hope this helps someone else as I wasn't able to find a reasonable cost solution.