 To promote ease of conversion, 'open' back models had cab bodywork that bolted to the chassis and could therefore be removed easily during the conversion process giving better access to the chassis under.On 'closed' back models this flexibility for conversion was not considered necessary as customers buying an enclosed van type vehicle were unlikely to require access to the chassis in a similar fashion as 'open' back purchasers.More likely modification of the bodywork undertaken by 'closed' back purchasers would constitute removal of roof panels for elevating sections or the addition of windows as can be seen in many motor caravan conversions for example.