PJ
Why drill through the chassis,personally I wouldnt touch it
I drilled through my floor pan and put a 2 ft6in approx section of angle iron under the floor and another above and sandwiched them together with 4 huge bolts with big washers and used the top one to tether the tank to.
Same here with old van, but maybe new van new plan.
Anyway I just wanted to help clear up the confusion, it definitely isn't classed as a modification, for anyone considering doing it that way.
I haven't decided what to do yet, going to have a chat with an engineer.