Plugging several TruDesign composite seacock skin fittings that aren't 1 &1/2" size...

I'm in the process of replacing all of our through-hull fittings with Tru-design composite ones. Three of our fittings are for now redundant but may be reinstated at a later date so I'm loathe to glass over them. I thought for these three that I'd simply install a domed Trudesign skin fitting, and then cap it off with a blanking plug (see image), however Trudesign only make a 1&1/2" blanking plug and don't make any other sizes. The three through hull fittings I'm trying to cap off are 1/2" and 3/4" sizes. I've discovered lots of PVC threaded plugs or nylon threaded plugs but none that are officially stamped for marine use. The temperature and pressure ratings ranges seem fine for these, and UV resistance shouldn't be an issue as they will be installed in the boat's interior and mounted below the water line. Am I worrying unnecessarily? Has anyone encountered marine certified 1/2" and 3/4" sized blanking plugs or would have any advice or commentary?