if you put the sub panel in attic space i really don't think it is a very wise idea at all because the tempture changes and humity involed in there and what more if the repair person do come in the house to find the subfeed some will not able to located that in attic ..
the other point the attic during summer time can get very hot in there and cause the breaker to kick out early than it should be and the tempeture in attic can go much as 140 degress which it can make the breaker kick out early pretty easy.
the other thing is in the attic is dust from insluation i am sure about this but some kind of insluation can be dangerous and if dust built up on the breaker it can prevent from tripping at all.
in my option i rather stay away from attic space for subfeed much as you can for few reasons as i say above there and the other part is if the power for sub feed go dead how the heck you will find it if you tie the attic light up there with subfeed circuit .
i am sure few other sparkys will say the same answer as i saying in here .
use the common sense to put the subfeed box
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)