Zero clearance help

This is my first post and I must start off by saying I have gained an incredible amount of knowledge just by lurking in the forums and using the ''search'' button. I have a Prefab fireplace that I am considering installing a Kodiak 1700 into. The insert dimensionally will fit but the fire place has about a 4" gap between the bottom fire brick and the floor. I know putting a 400 lb stove would crush this and needs support. I have a few ideas on how to support the weight of the stove, but the radiant heat is my big concern being it now only has a sheet metal cover over the wood floor.Is this even doable or can I line it with brick as a insulator? Any help from the pros around is greatly appreciated.