Unlike the old LDVs (Leyland Development Vehicle) where the cargo bay floor-pan had nice wide ridges and narrow channels, the engineers at Ford, in their infinite wisdom, decided to bestow a range of widths to the ridges and channels and just for good measure there are even two different ridge heights! To add to the fun the surface area of the ridges (for screwing into) is significantly less than that of the channels.
I decided to take advantage of the increased channel area to install under-floor insulation – for acoustic as well as thermal insulation – prior to laying the ply floor. The insulation I opted for was the regular thin foam sheets used with laminate flooring which is easily cut into strips that can be laid into the channels. A layer of aluminium baking foil was then glued to the underside of the ply as an infra-red reflector prior to screwing the ply down to secure it.
To reduce weight I opted for 9mm ply, however this may prove to be something of a false economy due to its greater flexibility compared, to say, 12mm ply. At this point the mere couple of millimeters difference in height of the two narrow edge-most ridges, in combination with the thinner ply, manifests in the form of a dip in the floor surface at the edges when a load is applied to it. This may prove to be insignificant, but if I was to do the floor again I would lay ‘joists’ in the channels to float the ply on rather than resting it on the ridges of the floor-pan.
Just to add a further frisson to the frustration the engineers chose to bend the outer ridges to accommodate the wheel arches making it even harder to lay any ‘joists’ close to the edges.
I am sure there are brighter minds out there somewhere that have come up with elegantly simple work-arounds, but in the meantime I offer my experiences as a heads-up note of caution to others with designs on converting a Transit.