Will do Jacob, very thoroughly I might add for this might have some use for someone else.
Regarding the construction, I haven't got the chance to see if these rails have wedged tenons which seems the norm on iroko doors.
Only finished the chores now, so have a little time to do a proper inspection.
Seemingly the tenons are bare from a peek of just one, but that doesn't mean that there might not be some filler concealed in the mortise.
I hope not, especially if these aren't through tenons. fingers crossed on that one.
Regarding sagging, that is surely the same with any door, and especially so with a
12 panel/wide door.
Indeed it might be a good idea to make "trunnions" if by that you mean a kinda
jockey wheel on a trailer.
I might do something like that, anything but a wedge under the door, as that is
evidently terrible for a door which might be getting water ingress from a sloping driveway.
Cheers
Tom