A method that I find quite nice for Canadian Climate change issues is mount the fibre print to 4 ply rag board and then cold mount this 4 ply mount to diabond. Very rigid and no warping, adds cost and weight but really a nice base to add on an over matt.
We are using more diabond for larger work where weight is not the concern in our frame shop.

FWIW this is how Mr Penn mounted his work, diabond was replaced with sheet of aluminum,, as well he mounted a thin rag paper to the back for his notes... very nice presentation