Generic Benroy floor attachment

Hi,
The Generic Benroy plans call for bolting the floor to the frame. Does this mean it is ok to drill holes in the chassis steel (mine will be 2x2 1/8 square tubing) or do I need to weld tabs to the frame and drill those. How much drilling can I do to a chassis before structural integrety is threatened?
Thanks.
Kris
The Generic Benroy plans call for bolting the floor to the frame. Does this mean it is ok to drill holes in the chassis steel (mine will be 2x2 1/8 square tubing) or do I need to weld tabs to the frame and drill those. How much drilling can I do to a chassis before structural integrety is threatened?
Thanks.

Kris