These rules are based on the forge world rules for a Tarantula in a game of 40k.

Tarantula Automated Turret
WS BS S T Ag Int Per WP Fel
-- 20 - 50 -- -- 20 -- --
Wounds: 10
Skills: Awareness (Per)
Talents: Heavy Weapon Training ( Bolt, Las, Melta )
Traits: Armour Plating, Machine (6)
Armour: none (all 8)
Weapons: Heavy Bolter (150m; –/–/10 ;2d10+10 X; Pen 6; Tearing, Twin linked), Lascannon (300m S/–/--; 6d10+10 E ; Pen 10; win Linked), or Multi-melta ( 60m; S/–/–; 4d10+6 E ; Pen 13; Full Blast (1))
Gear: unlimited rounds for what ever weapon is chosen.
*BS cannot be increased by firing full auto* *will fire at the nearest target* *if equipped with a Multi-melta or a Twin Linked Lascannaon it will always fire at the biggest target over the nearest*

10 wounds seems awfully low. I'd say double it to 20 and call it good, the minimal armor it has would make it extremely easy to destroy by either friendly fire or from a foe in most instances.

BS of 20? That seems a little low to me. 35, maybe?

Wouldn't it be more appropriate to stat it as an immobile, CCW-free Battle Servitor with slightly better armour? The behaviour of the Tarantula could be modeled by ruling it can only engage Overwatch, rather than firing normally (so half max range, firing at targets as they appear, etc.).

I too think the skill should be a bit higher although the +10 for full auto will help. The other big question of course is how much requisition to have them cost.