In theory all the vehicles could fit into one module. 10t for the ATV, 8t for the G-Carrier, 4t for the air raft and maybe 2t for both bikes. That's only 24t total so strictly by the numbers we'd have 6t to spare.
But at some point logic kicks in. How do they get in and out? Is there enough room to move around and board these vehicles? And even though the numbers add up, their shape and size hasn't really been taken into account.
(will repost that pic I sent to you here.)
In my scribblings I actually went for a 4square by 3 square by 10 square. If we're working with 4squares equaling 1 ton then that comes to exactly 30.
My main thinking behind 3 square height instead of 4 squares is that the cutter itself could be 4 high by 4 wide, but if the module itself is only 3 high it would allow for the spine of the cutter. I tried to illustrate that idea in the central "cross section" images above with both a cylinder and a rectangular module. The black part at the top of each module is the spine of the cutter.
I think the theory behind the ATV module is that 10t is taken up by the ATV itself, and the rest of the tonnage allows access to and maintenance of the vehicle.
From High Guard p46:
Hangar: Normally, when a small craft is included in the design of a
larger one, it is installed into a form–fitting enclosure in the hull of
the mother vessel. The scout’s air/raft, for example, is carried in a
small compartment in the forward section, with barely enough room
for passengers to scramble on board. Most repairs and maintenance
require the air/raft to be launched first.
Adding a full–scale hangar allows for repairs and maintenance of
the small craft when they are back on the ship. The hangar includes
spare parts and specialised testing and repair equipment for the
stored craft.
A hangar requires 30% of the space allocated to the small craft, and
costs MCr 0.2/ton.
EDIT: Went to bed with a headache last night. Forgot to finish this...
So according to High guard, if the module is going to act as an actual garage then we need to allow an additional 30% of space for shuffle room and workshop space.
For the image on the right the box representing the G-carrier is really just a place holder. Because it's a 24 square space, with a 3m high roof that makes for 12 tons ... which I figured would easily accommodate a G-carrier. With High Guard's "+30% gives you hanger space" rule then there would even be room to move around and perform repairs. A 12 ton area could also accommodate an ATV. An ATV "hanger" would require 13 tons however. If the module was a rectangular one with a 4.5m (3 square) high roof like in the lower central image then you'd easily have enough space for an ATV hanger. This is where it comes down to the actual dimensions of the ATV. Most modules are portrayed as having a hatch on front leading to the bridge and a hatch toward the back leading toward the engine room. We wouldn't strictly have to stick to that (I doubt the fuel module does) but if we did then itd be good to figure out how the ATV exits the module. G-Carrier isn't such a headache. It could drift in sideways. ATVs need ramps and turning space if they come in from the side though. So maybe if we're having a "garage" module we'd want one with a big roller door on the back or something. Would mean the ATV could only leave the module if it the cutter carrying it was detached. Either that or we could have a hatch on the module's belly and have a big claw release the ATV, dumping it on the ground as the Cutter hovers above. That would look sweet! Dump and run kind of thing.
When we're speaking strictly about volume, both grav bikes displace less than 1dton. So with them it's really just a matter of figuring out how they're stored. I figured they could be mounted on wall racks and made to hover down near the exit when needed. They could also be coupled to the ceiling so that they float down when unfastened. In the pic I just put them there in the open area as if they were "ready to go".
If we're going to keep the ATV, getting all of our vehicles into one module may be a bit of a stretch, but I think it could be done. There may be situations where grav vehicles are no good. High winds and such. Maybe it'd be easier to have the G-Carrier hangered in the "Drop Ship" module seeing that it's more of a combat vehicle, and the rest of them in a "Garage" module?