Drivers side sill rusty,boxer symbol 2003

The sill on my autosleeper symbol needs repair,but useually the first to rot is the kerbside,which indicates rot from inside,the worst area is directly below the shurflow water pump....My question is,has anyone got experiance removing the water heater and diesel heating unit along with the shurflow water pump so access is available to the rear panel and welding maybe safely undertaken......Any hints and tips will be greatly appreciated on gaining access to the side of the van...Thanks in advance for advice...

The floor, side panel and sill around the water heater on our Duetto had to be repaired due to condensation and leaks from the heater. The repairs involved taking the bench seat out and the heater by the repairer. 
A friend of mine is a vehicle welder and restorer and tries to avoid Campervans because of the amount of work involved making the area safe to weld. Autosleepers are no worse than others to remove the trim and fittings. I am sure a careful check will reveal what needs to be removed.