Finally, the test drive of the chair is completed with a great success in the stern conditions of Mojave desert (California). See the photo set of the construction details explained below.
The transformation time I'm getting is less than 20 minutes from opening the trunk door to getting in the chair. However, I have in mind several easy enhancements for particular elements used in the construction, which might halve that time easily, while also removing one of the hand tools out of two required for transformation completely.
The assembled weight of the chair is equal to the assembled weight of the cradle, minus 3 styrofoam inserts and equals to 17 pounds (~8 kg). There are some possibilities for improvement there too, but I felt comfortable enough with that weight while actively observing various objects for 6 hours straight, moving the chair around and adjusting its height often.
What's left to do is to apply some protective finish (more on that later) to all of the surfaces, to add a permanent soft sitting pad, and perhaps a soft backing. So far a folded several times yoga (gym) mat worked just fine for me.