Looking thru ebay it seems there is a great deal on a hot tub attacked by mice, looks mainly insulation. I have not had this problem but how can it be prevented or can it.

to prevent mice and other critters, even some insects, use mothballs in the cabinet. The only downside to this is you may get that smell each time you turn on the blower (if equipped).

Another alternative is Cling Free dryer sheets, put a few in the equipment bay. The mice do not like that clean fresh smell.

Myself I prefer a little back powder and a ball bearing on a mouse trap. This process can be a little messy though.