First of all, thank you for all these awesome suggestions and links, especially to Officer Vic who followed and helped me all along, I checked them all out. Tank you to davelaric for his/her suggestion, it is great, but I don't think the roof is quite accurate. Just a public notice, I will put this mission on Officer Vic. I do appreciate all the effort all others put in, but I don't see the point of a lot of people stressing out over the same thing. In rough words, I will not accept any other skins, sorry! Also an update for Officer Vic, the top the ambulance is plain white, at least, the one I saw was. Secondly, Officer Vic, if you will post the skin, please give me a link to the model, thanks!
p.s. Sorry for the late reply, I was off to some place without internet! :)