I was looking for something to capture the water from an occasionally dripping radiator valve, and existing / commercial valve covers typically focus on the aesthetic aspect, but have holes in the bottom (guess to allow different mount directions).

I've sketched this in Tinkercad and it seems to work well.

The lock needs to be placed into the holes in the support beams, and then it fits snugly against the valve bar. The back of the box should rest on the wall and /or the bottom may be supported by the floor skirting boards. If it doesn't, you may need some extra padding. The cover dimensions fit typical European 2-pipe radiator valves, 3/4'' x 1/2'', D=50mm.