Serge,
That's right, the reason these armored vehicles are referred to as "Sandwich" trucks is due to their type of armor. Shortages of proper military-grade metal armor neccesated the use of alternating layers of lower-grade metal/plywood armor. Sand, cement, rubber and even glass were also used. Many types of truck chassis were used, including 15-, 30-, and 60-cwt CMPs.
See the book
Military Briefs 6: Israeli Improvised Armoured Vehicles & Jeeps: 1947-1949 for more detail.
