Run init rc script after package manager have loaded

I'm writing an init service which make sure a package is installed and if not, it will install the apk. The problem is, that currently I'm using a boot trigger with on boot but when I run pm install from there it doesn't seem to work. I've used a sleep command to wait for the package manager service to load but I would like to find a proper solution. I've had three ideas which all seems to lead to me to a dead end: 1. wait for a prop to show up, but the package manager service doesn't create any. 2. wait for a file to show up, again no such file exist 3. set my service in a class but it seems to be relevant for the service itself and not the trigger or am I misunderstanding something? My current service definition is like so: on boot exec_background -- /vendor/bin/install.sh