http://www.unicell.com/pdfs/Aerocell_GM.pdf
There is a picture of a 4500/5500 series Aerocell in this pdf brochure. You will also find some basic information regarding cargo box lengths and widths.
For more detailed information I suggest you call and ask for Jennifer. Tell her that you are being referred by David Hall. We have a good working relationship and I highly recommend her.
Jennifer will give you top shelf treatment.
Disclaimer: The use of the term "top shelf" is in no way a reference to the term "Top Tier". Unicell is a "Top Tier" manufacturer by default. Supreme Body Company is the only other manufacturer that has a somewhat aerodynamic cargo box compatible with the chassis referenced in the above post; therefore, with only two from which to choose...they may both have the honor of being top tier.