Separate chassis on vans & pickups

[dp]

What was the reason that the vans and pickups had separate a chassis but the non-commercial vehicles didn't?

Was it strength because I'd guess a Traveller could be as loaded down as a van?

Ta

[bigginger]

Because they were designed by somebody else (not Issigonis) and had to be capable of being sold without the rear bodywork so they could be fitted up/out to the customer's needs. It also meant that different (and better ;) ) rear suspension could be used

[rayofleamington]

Was it strength because I'd guess a Traveller could be as loaded down as a van?

yes - strength, but also flexibility as BigG mentioned.
The traveller has a fairly floppy floorpan and needs the wood to maintain stiffness.

The van probably could have been made monocoque with a bit of effort but to cope with the pick-up & bare backed versions there was a need for a chassis anyway.

In the early days, monocoque was in its infancy anyway so they may have struggled to get the massive contracts with GPO etc... without having a conventional chassis.

[dp]

Then was the monococque used for to keep production costs down?

[rayofleamington]

Then was the monococque used for to keep production costs down?

It was used for a lot of reasons - one of which was for stiffness. The guys at morris had spent a lot of time and effort to see how to make a stiff shell. (Stiffness is needed to maintain the suspension geometry under load which is one ingredient of good handling).
They were looking in exactly the right direction and hence the world only got evolution of monocoque design for the next 40+ years.
The modern monocoque is a tribute to those handful of innovative guys back then working at drawing boards and in 'the lab' (probably whilst wearing tweed and smoking pipes).

Revolution is only just on us again with composites and multi grade steels being used to increase strength but still reduce weight of a car body shell (various things have been done to panels for a long time, but it's only recently that multi-material grade shells have become mainstream)

[wibble_puppy]

probably whilst wearing tweed and smoking pipes

and using slide rules for all their calculations

[bigginger]

Poor swines. I was made to learn how to use one of them at school