The next decision was which securing method to use for the aluminium angle. Welding is generally considered to be gold standard however a few boat welders I spoke to said to stay away from welding if possible as they have seen some disastrous results, specifically cracked hulls.  They also recommended using the aluminium angle and place it down on the ribs then secure it with rivets. After some investigation into the rivets I found quite a few people doing exactly this. All the details here