Having done simular things in Somalia - plan for the worst....
That said - the NEC does not apply to this field condition IMO, and even attempting to apply resi calc factors would be short selling the fact that you are not dealing with normal people in normal conditions.
One can assume this - that after any formation - there will be shifts of several hundred taking a shower, then cranking the heat, as well as the space heaters sent from home, and that electric blanket granny sent, there will also be two to three TV's and boom boxes and every single light on. Since there is a fridge (all will open simutainiously) - figure there are microwaves being shared in each.... Then there will be the next rotation for chow and showers etc is 45 minutes later. This will last from 16:00~22:00!
So I say shoot for 100% and factor 125%.... Once you have that - periodically amp out the feeders at say 18:00 (6PM) - size your eventual transformers for 125% of that.
While the generators are running.... parallel several early, then back one or two off-line so the ones that are left are pulling 80%. You'll be surprised at what comes out of a generator that has been wet-stacking all day - in just an hour or two at 80%+ while 500 jarheads are doing their best to max it.... (If you want it busted over-night - USMC) If your stuck with some navy unit, or AF units one can assume less abuse in the fact that they are not trying to tap into the electrical for bizzare entertainment reasons (As Marines would) - but they have more creature comforts for some reason - I assume they are closer to their mothers and whine for more stuff...
Since I assume you do not have a load bank - use your load as one. And if you feel comfortable with it - you can load bank them against each other by paralleling them and backing of either the throttle or voltage regulator slightly.
Yes, I was an 1142.