Question about insulation material for Dickinson Heater install

[rkarakai21]

Hi all. My partner and I are installing a Newport Dickinson diesel heater in our Roughwater 33. We are just planning out and thinking through the installation. Dickinson Manual says either use 1/4" insulation with the stainless offset backing plate or 1/4" insulation with ceramic tile. We'd like to do a nice tiled panel for aesthetic reasons and for the insulation I thought immediately about 1/4" fireproof Hardie board (concrete board), the only downside to this will be the weight of course, as the board will be roughly 3' 6" x 14" or so, plus the weight of the tile and grout on top.

Obviously whatever we bond the tile to cannot be flexible, but are there any other types of fireproof backing board that would be lighter but rigid enough to bond tile?

What have you guys done on your heater installs?

Thanks

Ryan