I always wear a vented jkt. here in Az.. The rain/thermal liners I wear unattached. Never could see zipping/snapping them in and out.
Seems to work just as well too.
For added heat or rain protection I carry a pair of BMG Ezeon pants and an old fisherman's rain jkt. for any downpours.
This works for me when using any of the various brand armored jkts that I wear.