I just did this project a couple of months ago, replaced my Whelen nav/strobes with Aveo LEDs. It wasn?t a huge job to take the wingtips off, lay up a few layers of glass over the holes, sand and repaint. My stash of West System epoxy from building was long gone, so I bought this small batch epoxy from West Marine;
https://www.westmarine.com/buy/west-system--six10-thickened-epoxy-adhesive--10287571?recordNum=20
One tube should do the job for a few layers of glass. I sorta dreaded the job as I?m pretty lazy, but this wasn?t a big deal.