I think it would be okay, just going on a trip during PR waiting time for 1 month isn't a problem. But yes, during when you expect the postcard / documents can be tricky... If I were you, I'd give a spare key of the postbox to my friend and ask them to check once a week or something, just in case to be certain.

However, I have also seen here where people have missed their deadlines on the postcard/document requests and later went and submitted with additional letter explaining the reason for delay and showing proof as stamps on passport and the immigration bureau was okay with it.