they both can be the same. you should find computer fans at 120mm or smaller depending on box
cut two holes on same side ( one at the bottom, one at the top) secure the fans in... make sure the exhust (one face outwards) is at the top *as heat rises*
this should work, maybe depending on the size a small desk fan should be placed horizontal to the plants ( to strengthen stem and to cool heat from lights)
let us know how this goes
cheers