Elf

Hi all, I need to install a new 300L cylinder into a passivhaus. Looking at the telford tempest, it has an energy rating of "C", so not the best (considering telford as it ticks off most of the other features needed). Im going to wrap it in extra insulation after the fact to improve the heat losses a bit. But I cant improve heat losses from the cylinder base this way. My question is: should i put any insulation under the cylinder, and if so - what should I use? My idea is to use some load baring insulation, put it direct on the floor and then put the cylinder directly on top of this. This would lower heat losses through the bottom - the only part I cant wrap insulation around after the fact. Is there any reason why this may be a bad idea? If I go ahead - Im thinking foamglass or maybe XPS insulation - but any other recommendation gratefully accepted, neither of these are ideal really so looking for other options to add to the mix. Thanks.