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@ If exposed to extreme cold then struck against a very hard surface with force, saving throw is -10 on die!
[guess : anyone with a NAC of 2 or less would qualify as a very hard surface.
IF a hard metal item is in the area (here, incl. spells that target a single person) of a cold attack,
THEN if it is struck against a hard surface later in the same round [same round = game school : DMG.9!], then apply the -10.
Would changing the 1 to an 11 for hard metal items be easier?
If hard metal items fail the 11 then they are in a 'danger zone' for the rest of the same round, unless, of course, they fail with a 1.

The obverse : a hard metal item that is in the 'danger zone' that is the target of a 'SUNDER' (sunder = 2cb or 3nb) has a -10 DMG.80.DMS.

SUNDER = 3. or 4. A lot easier than tracking HP!

2. Crushing Blow (rule of thumb : a blow from 18.00+ Str.)

Do protective items extend their protection to items carried?
Yes, 2 two reasons.
1. It makes things easier (another step towards game school : DMG.9) by pushing the items to a point of 'immunity'.
To determine an item's POI, subtract any constant modifiers from the numbers on the table at DMG.80.
A result of 0 or 1 is a point of 'immunity'. Remember that a 1 always fails, hence the 'single quotations.

For example, a "leather [item] or book" would have the following points of immunity : f, e.
A "leather [item] or book", carried by someone wearing a +3 ring of protection, would have the following points of 'immunity' : cb, nb, f, nf, fr, e.

If it makes things easier, you can list the POI abbrev.- next to the item's ENC, or whatnot.

Rationale : Why does this make things easier?
When items are destroyed, a character's total encumbrance (at least) has to be adjusted. The more destroyed items, the less playability. Less playability, less time spent in game school (DMG.9=220).
Isn't this just a new rule [in the spirit of 1E, no new rules?]? No (see reason #2.)

2. See DMG.81.DMS. This isn't a rule, so don't apply it if you have a reason not to. POI are a BTB implementation, nothing more.

    Also, a note on items <mirror this one, elsewhere> : if you are using item saving throws, then it might be a good idea to have a separate sheet for items in containers. With multiple containers, prefix the item with a CAPITAL LETTER that corresponds w/ the container.
    Also, place as many permabjurations on your container as possible (if new item permabjurations are researched, go easy on the spell level, and be happy that you have good players! Any spell that increases the playability (DMG.9) of the game is in the spirit (DMG.220) of the game, and should be encouraged, to the point of being as generous as possible with the level of the spell. An extension of this general principle would be the use of 'power' and 'alteration' components (not a new rule, at least insofar as MU spells go : PH.64). 'power' components could give certain spells a permanent duration, and 'alteration' spells could alter an AoE from 1 person to 1 item ... If doing so increases the playability of your game, then go for it!)

EDITS
Passive, 'No' : Game school (DMG.9) : I wouldn't apply @ to items that are struck (ie. passively).
Active, Yes : Apply the @
In other words, @ only applies to active strikes : usually, a READIED weapon that is used to attack in melee.]
I would apply a '-2' (DMG.81.DMS) to the 11 if the force is that of a crushing blow.
In other words, in a 'SUNDER' attempt, this . Instead, give a DMS (DMG.81.DMS). Would this make things easier?