Mekboyz have an uncanny understanding of battlefield technology and will sometimes build or scavenge powerful force field projectors to protect the Boyz on the battlefield.
A kustom force field gives all models within 6" a 5+ cover saving throw, vehicles within 6" are treated as being hull down. The force field has no effect in close combat.
Errata — Chapter Approved: Codex: Orks Q&A (v1.0): The kustom force field counts as a two-handed weapon for the purposes of limiting what its Mekboy can carry — it's a bulky piece of equipment that needs two hands to operate, even though it isn't really a weapon. Its 6" range is measured from the Mekboy model himself, even if he's riding in a vehicle — not from the vehicle. For a vehicle to count as being within range for the hull-down effect, the entire vehicle model must be within 6", not just part of it.