Cheers Downhilldai. I'll bolt it on as suggested. I hadn't thought about someone grabbing it, but i can see it makes sense for it to be fitted securely.
Thanks 9D280 regards bolting through the transom knee - I hadn't actually considered that.
I thought it might interfere with the steering arm on the Twatsoo at full lock, but it doesn't. Just tried it, so far, so good. What about the actual area for mounting? The transom knee measures 11" high x 11" deep x 2" wide. What are your thoughts regards the mounting plate? If I use the transom knee (area between tube and knee) and get a plate made that fits the area with 4 mounting holes and the lower section of the light pole welded so when fitted rests against the transom?