just an fyi, for the 1009 owners not necessarily the 1008.
The reason for the tube doors is the same as keeping your doors on. These bodies are not made to run with the doors off. heavy off road driving with the doors off will stress the body and twist it. The tube doors keep the hinges and the latch locked together like the regular door but gives you the feeling of no doors.
After a hard off road trip with the doors off on a blazer body, they may not go back on.