A made this about 30 yrs ago to match a latch lap with trellis fence:
It was a simple design of 4x2 rebated to hold a partial panel, jointed with half laps at the corners and reinforced with a horizontal strip and a diagonal strut. I used softwood apart from the top capping and it’s survived reasonably well.
With the erection of a new close boarded fence it was time to renew with a new bottom rail, strut and horizontal strip.
I’ve still got the bottom hinge to refit as it got bent during the dismantling process.
The green Ronseal fence paint is awful, hopefully it will fade soon.
Rod