I require some means of carrying my windsurfer on the roof of my camper as it's turned out to be just too darned big to fit inside. Should have thought of that when I took up this sport

Any suggestions on where I can get some roof bars preferably please?
I have a 1990 Holdsworth Villa (photo below).
It's a 300mm distance between the gutter and the top of the roof. I haven't managed to find anything that big.
Any help would be really appreciated. I'm hoping to set off on a bit of a UK road trip and I'd like to take the windsurfer with me

Anita