The clamp post works - but definitely need to add floatation aides (on my last wave it did get knocked off and I had to look for it (PHEW!!!). A camera float and some additional lengths of pool noodle should do the trick. I may try the bigger clamp just so there won't be any shifting. Here are some of the pictures from yesterday afternoon.
This was on a super full tide - the waves were tiny - but the funny thing about gopros - waves and bellies can look way bigger than they really are ;)
But like I said earlier - this is a view that you only want to shoot a few times - after that it can get a little repetitive (even the paddle mount I use when SUPing suffers from that now).