[broadgage]

As has already been said, rigid insulation board may be affixed directly to the inside of the metal walls, and this insulation board may be further lined with plywood.
If heavy shelves or equipment are to be fitted to the plywood this needs to be substantial and very well fixed.
I would bond the plywood to the insulation board with adhesive, but would not rely only on the adhesive. A length of substantial timber around the very top of the wall that is bolted through both the plywood and the insulation board to the structure will resist any tendency for the plywood to fall inwards.

It might be prudent to first paint the inside walls with a suitable rust inhibitor.

The void between the metal walls and the insulation should be sealed from the relatively warm and humid internal space, so as to reduce condensation in the void. Some condensation is still likely, hence my suggestion to apply rust inhibitor.