Robbert,
I looked through my copy of "German Military Trailers and Towed Equipment, 1935 - 1945," by Horst Beiersdorf. I did not find the trailer discussed. However, in the book it states that the Germans used a lot of different types of trailers without ever assigning them a designation.
I found a discussion of the history of Fallschirm-Artillerie-Abteilung 7 on the Axis History Forum webpage.
This is the link address:
http://forum.axishistory.com/viewtopic.php?f=83&t=184345&sid=6753c7edba2d68208f1467ea185deec8In the discussion a photo is shown where the unit received the trailers at the same time as the kettenrads to tow their artillery:
"In the summer of 1940 it was expanded to a Fallschirm-Artillerie-Abteilung 7 (parachute artillery group) within the 7th air Division. Its weapons were upgraded getting the Gebirgsgeschütz 36 (36th Mountain Gun). In March 1941 the 2. Batterie was upgraded with the new light gun 40 / 2 (LG2) of 105 mm. The recoilless gun can be broken down into 4 packs and could be dropped by parachute from the Ju52. It was towing with a BMW R75-Beiwagenkrad which was dropped in a quintuplet-parachute. The howitzers used in the 1. and the 3. Batteries could not be dropped by parachute but could be loaded only in a Ju-52. The newly introduced Kettenrad HK 101-SdKfz.2 serves as a traction device."
Two other photos were posted showing the trailer on Crete:
These photos posted for discussion only.
Don't know how much help these photos will be. I would make an educated guess that the trailers were discontinued after the decision was made to not use the FJ in an airborne role again with the FJ being reorganized after the Crete invasion. Good luck with your research.
John