I looked at ambulance boxes. The two issues I found were a lack of height and thermal bridging. ...
lack of height issues is a fallacy many fall for. Loww height is only in first one or two of the three Classes of Ambo's if I recall right. Not that hard to work around if one wanted too though.. (rolling stools/chair) . Have a nice awning room and outdoor cook setup to go under it. Commonly many cook outdoors on family outings like this anyway.
For full timing..... though you would want one of the Medium Duty Ambo' boxes and those are made to be "stand up" ambo's. Also they fit on Medium Duty truck chassis same as LMTV dimensions. Shortest height of these a 5'8 person fits fine (Tis what I got cause wanted low trail height) .... and the tallest of these (usually swat, search rescue , wildfire personnel transport , dive teams, etc..) are set for handling folk up to a little over 6' if I recall right.
Thermal bridging- again a bit of a fallacy. Less than a 1/4 of exterior walls are fronted by interior wall if keep the exterior /interior storage (part of its strength so you should anyway). Exterior storage space pretty much would eliminate issue with thermal bridging cause of their depth. Newer the models... and the best of the builder's from say 2000's up I do believe have thermal bridging material built into them.
sizes... up to 16' long I think. Mine is 14.5 M1079 is 12.