I’ve been thinking about this recently too – not seen any advertised but would probably look to make it myself anyway. I was thinking that if the boom was rested between the rear tank and the aft end of the foredeck it could act as a ridge to support the cover just higher than the sidedecks. It wouldn’t be too difficult to then take a series of measurements from the boom to the gunwhale to generate some form of pattern. In terms of attachment I was thinking of hooking it onto the tent bridle just under the gunwhale. I had also wondered if it could double up as a towing cover but that would mean it would need to be a quite a bit more robust. Anyway I dont know if that all makes sense – would be interested to hear from anyone else who has made their own and also to hear how you get on.