[Fyron]

A sample of what AT just said, making colony module only fit on colony hull. I made it take only 30 kT, but at 3000 kT, no ship can mount it normally.

(ignore the whole natives thing)

Make sure to use a dummy ability to supply a tag explaining the need for a scale mount, as shown here. It helps to alleviate a little bit of confusion.

Name := Rock Colony - Rock Natives
Description := Materials needed to start a colony on a rock planet.
Pic Num := 54
Tonnage Space Taken := 3000
Tonnage Structure := 200
Cost Minerals := 4000
Cost Organics := 4000
Cost Radioactives := 4000
Vehicle Type := Ship
Supply Amount Used := 0
Restrictions := None
General Group := Colonizing
Family := 5001
Roman Numeral := 0
Custom Group := 0
Number of Tech Req := 1
Tech Area Req 1 := Rock Planet Colonization - Rock Natives
Tech Level Req 1 := 1
Number of Abilities := 3
Ability 1 Type := Colonize Planet - Rock
Ability 1 Descr := Can colonize a rock based planet.
Ability 1 Val 1 :=
Ability 1 Val 2 :=
Ability 2 Type := Cargo Storage
Ability 2 Descr := Provides 20kT worth of cargo space.
Ability 2 Val 1 := 20
Ability 2 Val 2 := 0
Ability 3 Type := Star - Unstable
Ability 3 Descr := Requires a scale mount to be used on colony ships.
Ability 3 Val 1 := 0
Ability 3 Val 2 := 0
Weapon Type := None

330 kT happens to be a unique hull size in my mod, so I didn't need any 1s digit tonnage to force uniqueness.

Name := Colony Ship
Short Name := Colony Ship
Description := Passengers of the Colony Ship venture forth to eke out a new settlement on uninhabited new worlds.
Code := CL
Primary Bitmap Name := ColonyShip
Alternate Bitmap Name := ColonyShip
Vehicle Type := Ship
Tonnage := 330
Cost Minerals := 150
Cost Organics := 600
Cost Radioactives := 0
Engines Per Move := 18
Number of Tech Req := 2
Tech Area Req 1 := Fundamental Physics
Tech Level Req 1 := 1
Tech Area Req 2 := Normal Race
Tech Level Req 2 := 1
Number of Abilities := 2
Ability 1 Type := Combat To Hit Defense Minus
Ability 1 Descr := Lack of maneuverability makes ship 20% easier to hit in combat.
Ability 1 Val 1 := 20
Ability 1 Val 2 := 0
Ability 2 Type := Modified Maintenance Cost
Ability 2 Descr := Base maintenance rate is 10%.
Ability 2 Val 1 := -90
Ability 2 Val 2 := 0
Requirement Must Have Bridge := True
Requirement Can Have Aux Con := True
Requirement Min Life Support := 1
Requirement Min Crew Quarters := 1
Requirement Uses Engines := True
Requirement Max Engines := 255
Requirement Pct Fighter Bays := 0
Requirement Pct Colony Mods := 8
Requirement Pct Cargo := 0

In the mod, there are a bunch of different colony modules, such as hybrids and universal, so I have more than just 3 families listed.

Long Name := Colony Mount
Short Name := Colony Mount
Description := Colony module used to colonize a new planet.
Code := CM
Cost Percent := 100
Tonnage Percent := 1
Tonnage Structure Percent := 100
Damage Percent := 100
Supply Percent := 100
Range Modifier := 0
Weapon To Hit Modifier := 0
Vehicle Size Minimum := 330
Vehicle Size Maximum := 330
Comp Family Requirement := 5001,5002,5003,5004,5005,5006,5007
Weapon Type Requirement := None
Number of Tech Req := 0
Vehicle Type := Ship