I'm guessing that is a pliable material? You don't say what the hole spacing is but a rail that is relieved on the back would be a better option, reducing the contact surface, then just tighten it down "into" the material just enough to be solid. We sell the BT15, looks like it is probably too short for your hole spacing but you can always relieve some material from the back of any rail.
You might have to remove any exaggerated high spots on the stock as well.