I fitted all the belly pans during my resto. The middle one is welded on but the 2 side ones I fitted by putting rivnuts into the chassis/sills. They were fitted as standard to my UK bus as it is a pop-top. I painted the whole underside first including the belly pans and then only ground away what was needed to weld to try and help with preventing corrosion. The underside was then cavity waxed and undersealed.
When I took them off they had actually done a pretty good job at protecting the underside considering it was a 40 year old UK bus but its horses to courses.
The middle one I got from C&C as at the time no one else sold them (dunno if his has changed) and it was a s**t fit, they were very helpful and swapped it out but the new one was the same so either my bus is different or the part is not measured out very well. Anyway, I chose to keep it, I had to slice a section out of the back of it and add a fillet, no big deal. There's some pic's here:
http://s837.photobucket.com/user/marktmaguire/library/VW?sort=3&page=16" onclick="window.open(this.href);return false;
