A friend of mine that is a driver gave me a shool bus newsletter. I saw one of the advertisments in it was for cargo boxes. I have no intrest in the company but thought they look like they might be a good option. Of course they don't list any prices so they may be too expensive.
I called them and they were very helpful. The prices are not cheap of course what else is in our hobby. The one door model is $695+ shipping and the two door is $1300+shipping and the three door is $1895+ shipping. He said this was the first time inquired about conversion info. He said they will sell to the public as well as schools. They also come in white.