Problem is emulsion paint is liable to be water based and possibly distort or blow the cardboard box. Have you thought about folding the box flat and wallpapering it? Most of us have half a roll of old paper hanging about, and a nice patterned one could look pretty good.
Dont use spray paint. , all you need is some nice gift wrapping paer, thats what is normally used for food hampers. Ive never seen them painted before.
Any gift wrap paper will do and if you dont want a pattern on it turn it over and use the other side.
sorted.!!!