Trailer rubber bung

I have a trailer with tilt function without having to take it off of the tow hook. Of course you can tilt any trailer as soon as it's off the hook, but it's safer with the tilt funktion to handle the weight still on the tow hook. While tilted there are no feet to protect the steel tubes from scrating on the tarmac. So last time I used it, the nasty scratching sound reminded me to do something about it. Otherwise the zinc plating would be damaged and the whole thing will start rusting sooner than necessary.
So I sat down and did something about it.
This is a bung for a 40mm x 40mm tube with 2,5mm wall thickness.

The hole in the middle is to make sure any rain doesn't stay in the tube and make it rust. I made it large enough so that adequate airflow should make it dry as quickly as possible.