john I have done that with other vans many a time for holddown rings and tie bars. Most important be sure there is nothing under the spot that you are drilling a hole! be very sure . and if you do, back the bolt up under the floor with a steel washer or steel plate. if you use any other type of brass aluminum etc, you will start a galvanic reaction and it will rust. also paint the drilled area with a zinc based paint and when you tighten the bolt up squirt some silicone caulk all over to make a seal that will keep the air and water out.if i was bolting down a heavy item i would back the bolt up with a longer peice of flatstock to spread the force of the bolt over a larger surface area under the floor.