Unclear on the size of the apparatus require to secure the 92 anti-protons - did it occupy the entire truck?
Of course, it's compact because it only has to last so long. CERN's press release discusses needing a generator and a cryocooler in the truck for longer trips: https://home.cern/news/press-release/experiments/base-experi...
This older article about the test they did with ordinary protons, indicates the outer frame measures "2.00 meters in length, 0.87 meters in width, and 1.85 meters in height" and comes in under 1000kg https://ep-news.web.cern.ch/content/cerns-base-step-leap-for...