I am more worried about the strap than the striker. My thoughts are similar on the striker except that I was not thinking slotting it through the bottom of the beam as I think any largish holes will tend to weaken it.

Do the dimensions I gave for the strap make sense or will the bar be overbuilt for a 16 footer?

I am not too happy about fastening the SS strap to the al beam directly because of corrosion. Any good ideas here or pictures will be most welcome

regards