render texture and mask problem

hey all

just wandering if anyone is able to help, ive got a render texture that is being rendered as a raw image on a world space canvas, however when i apply a mask to the canvas (needed to hide the elements that slide in and out of the canvas like collapsed menu buttons etc) the raw image is put onto of all the elements within the mask. the raw image needs a unlit material applied to it to be displayed as desired.

Im guessing i need some form of custom unlit shader but this is just a guess and would have no idea where to start with it.

any help would be greatly appreciated