We're having our driveway gravelled (standard hardcore + 15-20mm
gravel method). There are two drain covers, standard rectangular
shape/size. Our builder isn't sure how to handle this. They could be
left to stand proud of/level with the surface of the gravel, but I
suspect they would look better covered. If the latter, what is the
best approach? If we just use the same or similar covers but lowered,
the gravel will probably move off their flat, smooth surface too
easily. He suggested a screed tray with some sort of material in it
to provide grip for the gravel above. Does this sounds reasonable?
Is there any 'best practice' for this? Any experiences to share?

Andrew.