I think that I might get a little op if it had health regen and no cons. :-/
But it would be cool if it only gave the metal boost which could be then a little higher.
That would allow some more flexible and sneaky tactics for the engie.

Pros:
+50% max metal capacity

Cons:
-Replaces Secondary weapon
+10% damage vulnerability from all sources

+50% Metal
+25% more metal in pick ups and gibs
Replaces the shotgun or the pistol
If pistol is replaced:
+15% more clip and ammo capcity
If shotgun is replaced:
+50%more ammo capacity
+15% firing speed
No negative effects

Where's the metal when you need 'em in this back pack of coures

Maybe a metal reserve, something like:

Press M2 to get all metal back.

Can only be replenished by supply lockers or maximum ammo packs after your metal is already full.

This would be extremely helpful, and i would actually use it.

Pros
Temporary metal upgrade
Reloading with Wrench will give you +200 spare metal
+50% regular metal
+10% damage resistance
You can throw down temporary ammo that works like temp metal
kills all F2Ps in real life and gives you 999 burning team captains and 100 keys
Cons
If you are killed and have any of the temporary metal/ammo on your buildings/friends, it will down grade them/take away the ammo, until it is at the original metal/ammo level, like what the red tape does, but only when you have temp metal/ammo on a building/friend.
-10% move speed
No moving buildings unless the metal reserve is empty. You're strong but not THAT strong.
Mechanics:
Spare metal and ammo is like overheal for sentries and guns, but it will stay there until you find more real metal or you die and lose the level(s) you built with the metal

How about this:
The backpack replaces the secondary weapon, but when selected, it activates a mini-sentry-type-gun in the bag that you control manually, while the normal sentry operates on it's own.
But to compensate, the regular sentry would either get a fire rate reduction, or be limited to Level 2.

Originally posted by Drake Darkrune:

I think that I might get a little op if it had health regen and no cons. :-/
But it would be cool if it only gave the metal boost which could be then a little higher.
That would allow some more flexible and sneaky tactics for the engie.

the negatives are that you loose a shotgun!

Pros
+100% metal capacity

Cons
Replaces Primary weapon
-10% movement speed

replaced by pistol
+%50 metal
-%10 movement speed

+50% Metal
+20 metal regained every 5 seconds
-15 Max health

Because of the larger load of carried metal, maybe movement speed would be an ideal disadvantage?
+50% Metal
-10% Movement speed
-Replaces secondary
I'll agree with The Pink Headed Fungus

Originally posted by The Pink Headed Fungus:

replaced by pistol
+%50 metal
-%10 movement speed

perfect

Originally posted by ragdoll pony:

Originally posted by The Pink Headed Fungus:

replaced by pistol
+%50 metal
-%10 movement speed

perfect

maybe a little more peneltys
-10%max building health

Originally posted by StealthNinja133:

Originally posted by ragdoll pony:

perfect

maybe a little more peneltys
-10%max building health

you already lost a pistol for it

+50 max metal

-15 max HP