The guns are limited if you don't have enough transport means 7.263.
If I read correctly: one can choose to not setup the Guns on map, and will get extra transports (with an exception for 81mm mortars). But otherwise, if setup on map, they are not limited by the available transports.
So if you plan on moving your Guns, consider not setting them up on map on the first date.
Also, 81mm mortars don't get free transports, but still need them to move freely (even though they can be dismantled and moved as heavy SW).
BTW - I like the way trucks and wagons are treated in this CG. With the "exchange for extra CSPP" option, they don't cost as much after all - wagons will even get you extra CSPP if you take care of them (2 Wagon sections will cost you 1 CSPP, and by sending 3 of them back you get the CSPP back and get to keep 1 Wagon).
As a side note: 7.172 mentions exchanging "trucks" for CSPP, does this mean only the type found in Transport sections, or any type?