The success of the Gurdergen species as traders is predicated on a number of factors; the design of their ships is certainly a significant contributor. Unlike its smaller cousin, the Medium Transport has both internal and external storage. The latter comes in the form of container racks able to pick up, carry and drop off significant weights and loads.
As with other Gurdergen vessels, the Medium Transport is unarmed, slow and vulnerable to attack. Ship captains generally keep to safe, well patrolled trade routes on which they do not need to rent an escort. Savvy captains are aware that the efficient external cargo racks make their ships even more tempting pirate targets; would-be raiders do not even need to board the ship to steal cargo thus can do so quickly with no risk to boarding parties.
The Gurdergen are often contracted to provide ad hoc logistical support to the USEF; when military ships working in deep cover in alien territory need resupply it is often safer and less conspicuous to use a Gurdergen ship than a military freighter. The Medium Transport is large enough to transport fuel, ammunition and spare parts through these ships are sought after by pirates eager to get their hands on military grade equipment.