I have a single hoop A frame on my sea rider 5.4 It works fine and does what I need it to holds the nav lights and VHF aerials.
I trhink a single hoop looks better on a 4 metre make it tall enough that you can easily remove the Outboard Lid. Also when you are wiring the lights leave a drawcord in the frame . It makes it easier to rewire or add mods. Also use marine grade cable. Oh yeah don't water ski from it!
Theres a good welder near our Skool (in the same yard actually) who is also a ribster so he'd know what to do
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo