I bought a centre section from C&C (well over a year ago I think) but I suspect they might be made by the same people. I chose to weld it on but bolt on the two side pans mainly because I understand the pans were fitted for strengthening when the roof was cut out for pop tops.
The bus survived 40 odd years in the UK with belly pans so I wanted them to go back on. With the side pans removable I'm sure you can get good access to the centre section with a cavity wax gun.
I fully painted all the underside and the whole belly pans and then ground down the paint where I was going to weld, there are pictures on my thread:
http://forum.earlybay.com/viewtopic.php?f=2&t=23320&start=60" onclick="window.open(this.href);return false;
The centre pan was a bad fit, I think it was too wide at the back of the bus where it starts to spread out towards the rear torsion tube. C&C were helpful and I went through a few conversations with them on the fitting and measurements, they changed it for me but it was identical. Eventually I just accepted it was a bad fit and had to cut and re-weld the rear flanges to match my chassis. My bus is a UK '72 if that makes any difference.
For the side pans I used rivnuts and s/steel bolts, putting rivnuts into the chassis and the sills. After all the epoxy painting and stonechip I had the underside cavity waxed (with the side pan's removed) and then undersealed.
Weirdly just noticed you are in the same neck of the woods as me, I'm in Horley. If you want to take a look at mine you are welcome.
Mags