True that hardibacker is not good for ground contact. I used some scraps for a retaining wall a few years back and after about a 16 months it became brittle and sort of shattered.
I have had it in place on a few roofs for 2 plus years now and it is still solid. You do need to paint it since it is water resistant not water proof. I find it to be cheaper than other materials like plastic signs or PVC. It is an alternative. Give it a try.
I’m not sure you can find hard backer board around here. I haven’t found it so far.
I did find 3/8 cement board so I will give it a shot. It’s going to be a metal roof over it so I’ll try attaching it with E8000.
Doug, you can use metal flashing without any backer. I paint mine so they don’t look so “industrial.”