The floorpan is rusted throughjust behid the passenger's seat on my 89 RS and i was wondering what all is needed to be done to fix this? i also want to do a custom floorpan.Like no rear seats and higher to accommodate dual mufflers

 

To just fix it, you could go with the por 15 kit. Check out www.por15.com . Car Craft just did a write up of how to repair rusted floor pans. As for customization. You can do anything as long as you know how to weld.