The chassis is considerably different in design to the standard Defender chassis even though it looks similar. The side walls are standard, most of the rest is bespoke. The additional rear load bed mounting was to take increased weights as the standard chassis kept punching big dents in the rear floor.
Chassis made after the production run (service chassis) are slightly different, later ones have a triangular reinforcement behind the front outriggers, none of them have the front round tube going through the main chassis walls as it is more costly to tool and produce although it is stronger.
The chassis wasn’t galvanised due to the additional weight it adds. There were also Health and Safety concerns about the gases involved in welding a galvanised chassis.
WMIKs made from the factory had two outriggers in the middle of the chassis instead of just one on a standard Wolf chassis. The second outrigger is to take the extra load of the gun mounting. Many WMIKs were converted from Wolfs and kept one outrigger.
The chassis on all Wolfs was sprayed internally with Dinitrol rust proofing.
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http://en.m.wikipedia.org/wiki/Land_Rover_Wolf