Floorpan repair panels

I have stripped down my S2 GTI

1) the floorpan has rusted through on both sides, the sills appear not to need replacing.

Where can I get replacement panels for the repair.

2) The car has been jacked up on the box sections below the front floor pans they are now mishaped - are these part of the structure or can I just leave them. I am not looking to do a show car job I want to use the car in all weathers and not worry about it getting dirty.

3) the previous owner appears to have got rid of the crap from under the car, what is the best rust preventer and sealer for underneath.

thanks

CrazyQuiff does them