Mitre joints

Hi all, after a little advice on mitre joints. I'm building an outdoor table and bench seats, and the legs for the benches are going to be s loop of timber at either end as opposed to 4 legs. I'm using 80mm square remilled messmate. Was going to mitre joint the loop but was wondering if I should reinforce the joints the with biscuit/Dowel/spine somehow? The benches will obviously take the load, and there will be 3 legs across 1800 span (would one either end suffice? I can't see just a glued mitre joint being strong enough but happy to be talked down in that! Cheers