Fixed the skill scopes for skills Armour Factory and Beasts of Burden, now the income bonuses apply correctly to Slavery buildings.
However, it would appear that Slavery building incomes were actually implemented to be lumped as city income, so the skills actually increase all city incomes. To balance the skills, the income bonuses are now 20% and 30% as opposed to 40% and 60%.
Tweaked porthole .bin file.

Modified campaign script, mod is now compatible with other mods that grant mounts to other lords and heroes on campaign start.
Changed scope of Slavery building income increase skills to see if it will now take effect.

Added modified battle_entities_tables with tweaked articulation radius for Marauder Chariots, Marauder Ice Wolf Chariots, and Gorebeast Chariots. This greatly increased their effectiveness in melee by allowing the horses, wolves, and Gorebeasts to attack models close to them more often.

Added porthole binary file, Surtha Ek no longer faces backwards in campaign diplomacy window and now uses the standard 2D porthole as marauder chieftain 03 variant.

Resolved issue where Surtha Ek's horse drawn chariot mount does not attack in melee (incorrect mount type in land_units_tables data used Norscan warhorse animation instead of Chaos chariot steed animation).

Fixed "The Hunger" ability and ranged damage resistance buffs not applying for Norscan Giant.

Surtha Ek's skills are:

Innate: Madness Reins
Enemy leadership -5 (Local region)
Armour +10 for Norscan Chariot units (Marauder Chariots, Marauder Ice Wolves Chariots, Gorebeast Chariots) in his own army
Vigour loss -30% for Norscan Chariot units in his own army
Leadership +5 for Norscan Chariot units in his own army
Upkeep -50% for Norscan Chariot units in his own army
Upkeep +75% for Feral monster units (Feral Mammoths, Frost Wyrms, Feral Manticores, Norscan Trolls, Norscan Frost Trolls, and Norscan Armoured Trolls) in his own army

Unnatural Vigour
HP +5% for character (level 1)
Vigour loss -7% for character (level 1)
HP +10% for character (level 2)
Vigour loss -15% for character (level 2)

Champion's Regalia
Armour +15 for character (level 1)
Melee defence +6 for character (level 1)
Armour +30 for character (level 2)
Melee defence +12 for character (level 2)

Spear Wall
Melee defence +20 for Marauder Spearmen, Marauder Hunters (Javelins) in his own army
Melee defence +10 for Marauders (Great Weapons), Marauder Champions (Great Weapons) in his own army
Melee AP damage +50% for Marauder Spearmen in his own army (5 -> 7.5)

Grisly Trophies
Marauder Chariots (horse), Marauder Champions units cause Fear faction wide
Movement speed +25% for Giant in his own army

Live Feeding
Norscan Chariot units gain The Hunger (regenerates HP in melee) in his own army
Giant gain The Hunger in his own army
Upkeep +25% for Feral monster units in his own army

Armour Factory
Armour +10 for Norscan Chariot units faction wide
Melee defence +14 for Norscan Chariot units in his own army
Missile resistance +33 for Giant in his own army
Income +40% for Slavery building chain faction wide
Upkeep +25% for Feral monster units in his own army

Beasts of Burden
Campaign movement +5% for character
Upkeep -15% for Marauder units (Melee infantry, skirmishers, horsemen) faction wide
Income +60% for Slavery building chain faction wide
Upkeep +25% for Feral monster units in his own army

Shattering Charge
Vigour loss -30% for Norscan Chariot units faction wide
Movement speed +3% for Norscan Chariot units faction wide
Charge bonus +14 for Norscan Chariot units in his own army
Weapon strength +15 for Norscan Chariot units in his own army