So how much space does a Raider or Frigate have to move/store trade cargo without buying any cargo bay supplemental componants.

What about with the two cargo bay supplementals in the main book. I know these ships are like a Kilometer long but a lot of that is used up for guns and such right? I'm trying to get an idea of scale so go heavy with the examples.

It's not explicitly mentioned in the rules (It's inferred from one of the NPC ships), but in order to participate in a Trade Endeavour you require a Cargo Hold of some description.

Scale is difficult to describe with these ships, so much of it is handwaved away, or taken up by the colossal vaulted ceilings that the Imperium favours, or hidden subdecks that the elevatus units stopped accepting calls to at one point several decades ago and everybody forgot about it.

As far as my games are concerned, it's something of a gentleman's agreement with my players and I that if they don't have a cargo hold they can't carry anything more than basic ship's-complement materials while if they have a cargo hold I won't pester them about specifics unless they get silly.

This debate has been going on for ages. Someone else delivered an enlightening concept in this forum about this very same subject (a search for it yielded negative results somehow Here is what I copied verbatim, so bear with me.

"Thinking about crew for the ships, I once measured out the dimensions of a Lunar class cruiser for my players over a map of Manchester (wherein we dwell). Its bloody huge. Given that the ships don't occupy one plane (as does Manchester) and that in all the literature has ships teeming with huge numbers of faceless crewmen, 96,000 doesn't seem too big for a cruiser.
Compare to my favorite comparison, the real world Gerald R. Ford class Aircraft carrier, currently one of, if not THE biggest aircraft carriers afloat. at 333m long it is 15 times shorter than a Lunar class, it has a crew of 4,660.
If we scaled up solely on length, then a Lunar with similar crew requirements should have about 69,900 crew. That's about 2/3 of the Lunars. Of course 15 times longer is not enough. The aircraft carrier is 77m abeam while our lunar class is 800m abeam. That over 10 times wider too.
Also from Imperial ship design compared to a carrier, Imperial ships are notably taller proportionally.

I've been doing up a crude scale map of my player's ship (secutor light crusier). It's dimensions are 4.3 km by 0.5 km by 1.0km.
Some fun facts so far:
It has 8 (known) compartmentalized cargo holds (just 1 component). each holds 4 millions cubic meters and is as long as the aforementioned aircraft carrier, almost twice as high and twice as wide. which means, as a cargo, it could roughly carry 32 aircraft carriers (though how you'd get them out of the ship…)
The ship's 'palace' (luxury quarters, library, trophy room and observation dome) has more floor space than the Place of Versailles.
the crew quarters is 1.5 km long, 50m wide and 100m high. If I assume 8sq m floor space is need for each crew (the same size as an apartment I saw in new york) and standard ceiling heights, then it would fit 200,000 crew ( I only need 50,000). instead I assumed the extra space was taken up with public amenities and larger homes for the officers.

When you work out very crude comparisons of crew density an aircraft carrier weighs in at 0.181 crewmen per square meter. A lunar class weighs in at 0.0024 crew per square meter. And that's assuming both ships are on a single plane. As we've noted, Imperial ships are taller as well."

I haven't compared this guys math to anything, but…….. Staying in the safe zone, you could probably fit at least 8 of those aircraft carriers in a (one) cargo hold. Happy trading people.

Come to think on it, this might be the problem I have when they say a Barracks component can only support 10k worth of troops. Houserule I did. 20k. I sleep better at night, so don't worry.