For me, the trust institution might be a counsel made up of ex-presidents - those who have had two terms or conceded after one - who have a role overseeing elections.
Those who haven't conceded would be excluded, of course.
The reason for this is so that the sitting president has no power whatsoever to control the election, to suspend the election result or to stand for a third term. None.
This institution might also exclude candidates from future participation who have attempted coups on previous occasions! [You'd think you wouldn't need that to be said, but, well, in the US you do].
Obviously, this is a model more like a constitutional monarchy, but with democratic underpinnings (ex-presidents as guarantors, rather then a king or queen).