Here's how to fight loads of metal slimes. Note: I'm not sure if this works in generation 2, but it definitely works in generation 3. On your team you need someone who knows Holy Protection (I used the son) and everyone else you want to benefit from the slimes. You can use the wagon. It also helps if you have someone who can attack several enemies at once (I used the daughter with the morning star).

First, go to the volcano west of Mostroferrato where you got the Circle of Fire. Once inside, use Holy Protection. This will keep away weak monsters i.e. every monster on the first level except the slimes. After that, just walk around until you bump into some slimes, but stay on the first level. Reuse Holy Protection when it wears off. My usual pattern was four slimes. One ran away on the first go, the others attacked and used frizz. The next go, two more ran away. I defeated the last one.

Note: Even though the slimes run away and dodge most of your attacks, it only takes four hits to kill them.