Can't advise specifically on the Iveco Cargo but I have done a lot of replacement of cab sections on the Ford Cargo (1981 onwards).
You can get complete new panels -e.g. floor pan, scuttle etc from main dealers.
You would need the following equipment:
Spot weld removal tool (small rotary cutter which you can mount in a drill chuck for cutting around spot welds so that panels or sections of panels can be removed). Draper supply these cheaply enough - and it's a good idea to buy 2 or 3 as the cutters do wear out or teeth get broken.
MIG welder
Spot welder
It may be possible in some parts of the cab to use pop rivets (preferably stainless steel rather than aluminium) but there will be some locations where you really have to spot and MIG weld it - e.g. around windscreen.
As well as the spot welder you need the right electrodes (i.e. a wide range of shapes are available to deal with different situations and to get into awkward places). the power supply for this might be an issue - i.e. if you are not in workshop and have to do this "in the field", you would need a generator with enough kVA to power the spot welder.
Its probably better from a corrosion prevention point of view if you can MIG weld as much as possible. E.g. if you lap a floor pan section, the overlap can be an area of Crevice Corrosion (otherwise known as a Differential Aeration Cell!) which traps moisture etc. If you could MIG weld the seam it might last longer.
Proper surface preparation for paintwork etc is vital as well.
It is also possible to manufacture certain replacement parts if you have the enthusiasm and the gear to do it -e.g. the pressed steel cab steps (on the Ford Cargo) can be hand made to near enough the original using very basic equipment.
You often see parts like this advertised on ebay - which is worth checking out, but beware - sometimes the people selling parts aren't always sure what vehicle they actually fit!
JD
March 2008