No rules for modules you say - that is very debatable. No construction rules perhaps but plenty of rules for the modular cutter and the modules it can carry.
"Three interchangeable modules are routinely available for the modular cutter.
The ATV module (which includes an operational ATV) is 30 tons. It can land (and retrieve) an ATV on a world surface from orbit. The module can serve as an ATV storage location, if desired. It costs MCr 1.8.
The fuel module, with 30 tons of fuel tankage, serves as a a fuel skimming vehicle and storage tank. It costs MCr 1.
The open module is a customizable frame with 30 tons of excess space which can be allocated to passenger couches, fuel, cargo, cabin, or staterooms. It costs MCr2"
"The 50-ton cutter is essentially of two piece construction: a 20-ton frame and a 30-ton module. The combination is capable of 4-G operations and carries a crew of two (pilot and gunner). The cutter has a four ton bridge installed and mounts a Model/1 computer. It is armed with a single missile rack. Total craft cost, less module: MCr 31.5.
When the cutter is operated without the module, it has a smaller total displacement and thus greater performance: its 4-G acceleration is increased to 6G.
The range of commonly produced modules covers eight designs. Each has its own purpose.
1. ATV Cradle. Carries one All Terrain Vehicle in a streamlined and shielded cradle; upon landing, the exterior shutters of the cradle retract and allow the ATV to be placed on a -world surface. MCrl.8 (including the ATV, which is of standard wheeled design).
2. Personnel Transport. Contains passenger seats for sixty personnel. MCr 2.0.
3. Cargo Transport. Contains cargo space for 25 tons, plus passenger seats for ten
individuals. MCr 1.0.
4. Fuel Skimmer. Intended to dive into gas giants and skim their hydrogen gas
for fuel. It may be used to dip water from oceans as well. Carries 28 tons of fuel.
MCr 1.0.
5. Assault Boat Module. Contains basic positions for 16 troops in two sections, each with a bottom mounted door. Upon landing, power spades scoop out emergency entrenchments; the troops jump down into the hasty foxholes and the cutter with module immediately moves out of the battle area. MCr2.5.
6. Pressurized Shelter. An independent living quarters module for eight persons, complete with galley, power supply, environment recyclers, and sanitary facilities.
This shelter is commonly used in the establishment of advanced site bases, or where the troops are expected to be away from the ship for extended periods; it can be used to increase living quarters and total troop complement on board. MCr 4.5.
7. Weapons Module. A self-powered, independent weapons mount with the ability to be fitted with a variety of weapons. This module is typically used to provide close support for the ship's ground troops. Equipped with a computer Model/1 for fire control and a triple laser turret. MCr 8.
8. Fighter Frame. This framework module contains attachments to hold four 6-ton fighters. The module, as installed on a cutter, allows quick launch of all four fighters for the protection of the cruiser. Unlike the other modules, the fighter framework module is not streamlined and the cutter mounting the module cannot enter atmosphere. MCr2.0."
"The fighter framework module is treated as a standard module for attachment and reattachment (see below). All four fighters may be launched simultaneously, and the process takes less than a minute. Fighters, however, reattach themselves to the frame individually, and each reattachment takes about two minutes."
"Deployment: The major drawback of the modular cutter design in the Broadsword class is the problem of timely deployment of modules. Each cutter can be launched in a matter of minutes. However, the handling of individual modules is hampered by the fact that the only access to them is through the cutter wells. In order to change a module, the following procedure must be followed.
Assume that a fuel skim module is currently installed in a cutter and that a passenger module is stored within the ship. The cutter leaves the well and detaches the fuel skim module, leaving it lying free in space. It then reenters the cutter well and attaches the passenger module. The cutter leaves the well and detaches the passenger module; it then reattaches the fuel skimmer and reenters the cutter well, finally depositing the fuel skimmer within the interior of the ship. At this point, the cutter can leave the well and attach the passenger module for needed operations.
The procedure can become quite a shuffling match, and the ship captain must give a lot of attention to the exact placement of modules for use in any current mission.
Having the modules in the correct positions can become of overriding importance.
The times required for performance of basic cutter procedures are shown in the following chart.
Enter cutter well- five minutes.
Leave cutter well- five minutes.
Detach module in free space- two minutes.
Attach module in free space- five minutes.
Detach module in cutter well- two minutes.
Attach module in cutter well- two minutes.
Move cutter from orbit to world surface- twenty minutes.
Move cutter from world surface to orbit- twenty minutes.
As can be seen, the procedure can take about 37 minutes to complete. Planning is thus essential for efficient operations. Of course, with two cutters, simultaneous operations are possible.
Troop and pilot boardings are best performed within the ship. Pilots should be embarked in fighters before the fighter framework leaves the ship. Troops should be embarked in assault boat modules or passenger modules before they leave the ship."
Hardly any rules at all...