Question on moving and address – no address as I will be temporarily outside Japan

I am currently on a student visa and will be outside the country for summer break for around 1,5 months. During that time, I will be moving out of my current dorm and entering another dorm right after I arrive in Japan again. So basically I will not have any address during my time outside Japan. The question is:

• should I change all of my addresses (campus/MEXT database, JP post bank, residence card, etc) to the new one (so like 40ish days before) before moving to the dorm? 
• what should I do with the 転出届 and 転入届 notice in 市役所？

Your help will be greatly appreciated!