this one is very easy, but you have to be fast, since there's only 1 chest in a basement.
little hint: Once per match, as soon as you started the trial, locate the basement but remember that the location of it may change everytime you load begin, basically there are only two locations in any map that spawn the basements, memorize then on each map so you can get to them faster, aslo, when going under the basement do not run or make noise, because killers are used to check if there's any trace in the end of the stairs, I've already killed alot survivors just because of this, stay chill ^^