If your tray is in 1 peice then the kit has all the fixings to fit it back on how it should be when it left the factory 
But if yours is fitted correctly and is just low due to the car being lowered it won't raise the cover up any past standard.
Neil
I seam to have all the covers, but the covers which go in to the wheel archers are held on by tie raps.
its defo sagging down, can push it up about 30mm.