So, I thought about it and I had another idea for fighting Space Marines.
As opposed to hoarding against them, or using just a bunch of AP 3-2 blast weapons, try this: Mimicry. Marines are basically super-tough warriors, with great armor. So, make your orks just like them. This is mostly a fun-based strategy, but it works. Instead of normal boyz, use ‘ard boyz. They are tougher, and their armor will make them far more durable. Nobz are a great choice to counter almost any close combat unit. Meganobz as opposed to terminators. A Shokk Attack Gun instead of a Thunderfire Cannon. Battlewagons in the place of Land Raiders. Just make sure everything is as tough as you can make it, and marine-like. Just for fun.
I’d be interested to see a matchup like this.