Keep the OEM air box and buy an aftermarket pre-cut cover. Just in case you need to go back to OEM to pass smog inspection. Some of us have failed because inspector determined it was modified.
Finding an OEM cover is difficult.
In writing this I have cut mine too. After watching SW's dyno test of it stock vs cut out air box. I was convinced, out came the Dremil
No issues with rain or washing, BTW. I wash my engine bay allot, OCD like that. ( I went from Coned Filter due to excessive dirt intake, yes properly lubed )