Hi Em Eye
Hope I am not too late to help out.
Not sure what kind of decorations you were thinking of doing on your cookies...it sort of makes a difference in the choices you have for icing.
I have made a few gingerbread men and houses whilst in HK and Sing, never had a problem with using normal Royal Icing recipes using egg whites. I have found powdered egg whites at the supermarket with only a little hassle...I had to do this for people who were a little iffy about using raw eggs etc. I haven't found the meringue powder tho...maybe a cake decorating place might help you out there. The sugar content in this icing normally acts as preservative. The only problem is possible "sweating" when faced with big changes in humidity/aircon, don't keep in fridge! The big advantage of using this is that you can make it various colours, spread it on, pipe it on, paint it, shape it any way you want and it dries rock hard and stays that way,not many other icings will let you do that. I think this is the best icing to use, you can flavour it too.
Here is a page with a couple of tips for you...
http://www.kitchengifts.com/cookiedecorating.html
The other alternative is to use a fondant type icing (you know like wedding cakes etc) and make it very soft first to mould it into shape and then it will harden. This can be hard work though! Once again if you refrigerate them moisture will form onthe surface if you bring it out into the humidity...however putting in front of a fan for a short while will dry it off.
The other choice is just to use normal old icing, just make it fairly thick and not at all runny. Colour it how you want and just use a hot knife to spread or pipe on depending on how you want to decorate etc. You cannot paint on this though as it is water soluble. Another disadvantage is that it doesn't last as long.
Have fun making your cookies...hope I helped a bit...let us know how they turn out.
