RVs with extendable side 'rooms' .

[swordtart]

I think the difference is that turrets can mount weapons that traverse and the side extensions don't.

There is also the implication that a pop up cupola already contains the crewmember. The idea is that the extension would not contain anything as it was deploying, but simply allow passengers to move into it once deployed.

If you wanted to limit yourself to a few spaces of passenger space and you could substitute a pop-up sponson for the side extensions if you wanted to, but it seems a clumsy solution. It also isn't really what I was suggesting. This is not (one or two) small sections of 4 spaces popping out, but a whole telescoping side. As an example see the Beauer-x-van. In CW terms this looks like it extends the majority of the cargo space in the van doubling it's capacity when deployed. Their telescoping caravan extends its floor space from 43 to 129 sq ft, in about 20 seconds. That is both more space than a pop-up turret and it is far slower than a pop-up turret extends.

As for space, passengers in buses take up 2 spaces (and 200lb) by default (and this to simulate they are PSVs and you need gangways and luggage stowage). I am not sure why passengers in trailers should take up more space, but RAW doesn't apply to 15' van carriers (or car trailers for that matter).

It is interesting the use of the phrase "...rather than one as in a passenger vehicle" given there is no definition of a passenger vehicle (and if anything the bus should be it, but it requires 2 spaces).

Further ADQ&A in 7-2 gives "Pedestrians take up 1 space when they're passengers. When peds are crewmembers (i.e., driver or gunner), they take up 2 spaces. Passengers on buses, mini-buses and other dedicated people haulers take up 2 spaces." This leads me to believe the states 2 spaces for 10 wheeler trailers is an error in RAW.

ADQ&A 6-1 also gives us "When the vehicle is designed, each passenger or crew member must be given a specific firing arc, either right, left, front, or back. The person may not fire from any arc other than this one. This does not apply to cyclists -- they have 360-degree field of fire."

YMMV

EDIT:
Your comparisons to pop-up turrets raises (tee hee) an interesting point. Ordinarily vehicles cannot target the top armour of a vehicle higher than their own weapons (so a turreted compact can target the top of another compact, but not the top of a van for example) - unless the target vehicle has a turret (or deployed pop-up turret) in which case it can be targeted (at -2). The same is not true of sponsons of course, they are in LOS if the side is in LOS whether they are deployed or not and it is generally better to simply target the side (at probably a +1 or better to hit) until the armour is gone and then target the sponson itself (at -2) to destroy the weapons.

Treating turret armour as the top armour was a bit lazy frankly and whilst it was forgivable when we were talking about cars (and the game was still trying to be simple - which is arguable). It makes less sense that shooting a (say) 1 space turret off the top of a 20ft trailer (or a 1 space sponson off the side) automatically destroys all the armour on that side. If you open a sun-roof for example you have only 50% chance of bypassing armour.

That is why I am less keen on putting more strain on already overburdened RAW.