In examining a relative's storage heater, attached to the ground floor
stairs in the hall, I found it was just screwed to 6mm hardboard which
had begun pulling over its nails.

The 110kg heater will be re-fitted to heavy studwork into 4x4 stair
posts.

What should the boxing in be made of - 6mm plywood, 12.5mm red fire
plasterboard, 6mm cementboard? Jewsons wanted £50 for 6mm cement-board
(might as well use two piece of £15 from B&Q).

Conventional 3-bed semi, boxed-in understairs. I plan on 6mm butt-n-
match MDF matchboard either side of the heater, simple rail above,
retaining the wallpaper further up the wall.