Anyone able to point me in ther ight sirection with how this would be done? I assume I'd need to use some OnDecayLike hook and then check if the item is a minicopter but not sure what hook or how to check if something is the minicopter.

Any help apprciated.

OnEntityTakeDamage should work fine.

// Prevent decay on MiniCopters with fuel.
void OnEntityTakeDamage(BaseCombatEntity entity, HitInfo hitInfo)
{
	if (hitInfo.damageTypes.Has(Rust.DamageType.Decay) && entity is MiniCopter && (entity as MiniCopter).HasFuel())
		hitInfo.damageTypes.Scale(Rust.DamageType.Decay, 0);
}

Thank you, I shall give that a go later :)