I have a recessed spoil board even while still having my design of the the hidden belt inside my metal strut.
This link is my initial LowRider build log, and it details my table both with wooden side rails at the start, and later switching to metal rails:
There’s no reason I know why using metal strut means you cannot have recessed spoil board, and also, my design for hiding the belt in a strut could also be modified to work without a strut, simply moving the belt down below a table lip.