Apparently, the Aviation Traders folks worked with EASA to define a special type of cargo compartment, known as a class F, during their work on Iron Maiden's touring airplane. Just what is a Class F cargo compartment, and how does it differ in safety properties from the large class B compartments used on earlier combi configured aircraft?
Here in this amendment to the EASA CS-25 it says on page 4:
... for a new Class B cargo compartment definition as well as design criteria for a new Class F cargo compartment type. This latter class of compartment was introduced because whilst it was concluded that manual fire fighting was not feasible for larger compartments, alternatives other than just the existing Class C were identified.
And a bit further on page 5 (emphasis mine) :
... Further, a new Class F cargo compartment definition is added, which is not limited in size and which provides the means to control or extinguish a fire without requiring a crewmember to enter the compartment. This proposed Class F compartment standard accommodates the carriage of large amounts of baggage and cargo loads on Combi aeroplanes as well as in compartments of smaller sizes exceeding the new Class B definition. New aeroplanes designs can take advantage from the variable solutions under the Class F definitions to ensure an acceptable level of fire protection.
And more concrete:
The AMC further provides guidance for usage of other fire protection means in the new Class F compartment such as Fire Containment Covers (FCC) or Containers rather than having a liner installed to contain a fire and to protect the critical systems and structure of the aeroplane.
I guess it's meant to allow storage of cargo in non-cargo areas (which do not have the adequate fire protection measures such as liners) if other non-traditional measures are installed (such as the Fire Containment Covers)