My experience was exceptionally different to yours. When Reynard sent their 903 and 933 carbon chassis to Mexico in the late 90's, the cars would not meet the FIA crash tests (as things had moved-on considerably since the early 90's). Through extensive testing, it was decided that side intrusion panels were needed to the side of the drivers head in the cockpit, the front nosecone, and the sidepods needed to be completely redesigned. Carbon Fiber with honeycomb was tested and considered, but ultimately polyurethane foam with carbon/fibreglass skin was chosen and easily passed the crash tests.
I know this, as I was a lead driver in the championship, and was engaged as the test driver for the updates. Here are some photos that I just took of the photos on my wall...if that makes sense
anybody familiar with the 903 or 933 Reynard will see the considerable differences.
By the way, one of the cars I used during the development was none other than Michael Schumachers championship winning F3 car. Interestingly, it had some illegal hidden modifications to the chassis itself from when he was driving it. The 903 chassis was known to have flex in the drivers compartment, and his car had a very thick aluminium plate on the floor that was bonded with epoxy and hidden with a layer of carbon. This would improve the chassis rigidity and also centre of gravity.