If you are going to use it for critter transport you need to consider cooling in summer and heating in winter. That can be as simple as solar powered fans or a battery powered heater and a cargo blanket, but it takes up weight and space.

The only other thing I will mention is that here in Alberta anyway, they are magnets for break-ins but the poor crooks and seemingly are stole more frequently than credit card numbers. The wheel locks, axel locks, hitch locks, chains etc I see on those things would not be out of place in a Houdini show.