is it regular cardboard...like from a cut up box?? or is is slick on one side (like the Wilton cake boards)?
If it's slick and treated, you'll be fine....straight dry cardboard and I think you're right about it going soggy...but I think that will be true of anything you put on it.
If it's not treated, you might consider covering it with contact paper before you cover it with the fondant.
Just thought i'd let people know what i did in the end. it was quite thick card (nothing special or specially designed for cake making)...about 3mm in thickness; needed to be scored to bend it. it wasn't treated or shiny on either side (although when i brushed it with water it didn't absorb it straight away!
The buttercream that i used stuck it to the cake like glue! (much better than the royal icing i tried) and after brushing with water, the rolled out sugar paste stuck to the board quite well too (i recon it would stay on even if held upside down!)
Quote by @%username% on %date%
%body%