as the above had said the corrugations take care of venting the space for you so I don't think counter battening is necessary. I was also trying to minimise the bulk of my cladding so I went smaller. Selco do treated roof battens in 50x25mm and 32x19mm. I went for the latter against Cladco's advice.
Bear in mind that they stamp these sheets out in lengths up to 6 metres, and people install is on steel frame agricultural buildings as a single skin with no board sheathing to add rigidity underneath. If you had a 6m x 1m length of this stuff it would weigh a ton and you would definitely want the supporting battens to bear some serious weight. For a 2mish shed it's really not a concern.
My walls are 2.4m to the eves so I ordered the wall sheets in 2.4m lengths and I spaced my battens from the bottom every 60cm up. So there was 5 horizontal battens across the height of the walls. My rafter legnth is 150cm ISH so I did 3 battens, one at eves, one at ridge and one across the middle. I then secured my sheets down every 4th corrugation.
CladCo recommend the 65mm hex screws that have the baz washer on them. These are best for the corrugated sheets as the baz washer is a big soft spring that makes a perfect seal against the curve of the cladding. However I knew that this was going to be too long for my walls so I used their 45mm screws which come fitted with a bituminous washer, designed for making a seal against their flatter box profiles.ive found this to be perfectly adequate and driven in straight they give a good seal. 11mm OSB plus 19mm batten plus 18mm for the profile of the cladding itself (the fixing always go in at the 'ridge' of the corrugation not the 'trough') plus the 2-3mm of washer and bitumine gives you about 50mm – plenty of meat for your screws.
Get a good 8mm hex driver it makes the world of difference!