Good advice there from jake-the-peg but may i also recommend that you squirt some silicone sealant in to the holes prior to pushing the timber onto them to help secure it to the protruding bolts thus eliminating tha chance of it working itself loose over a period of time .. AND REMEMBER this is very yes very important !!! that that under the building regs you must not install combustiable material within 650mm above the burner of a gas fire not from the top of the appliance but from the burner.