I have a soft fabric case that I keep my Macbook pro in which I requested at the place I bought it (in Jakarta). It helps prevent any scratches / cosmetic damage while in my backpack.

I've never really had an issue with leaving it on my bed at a hostel. If you're not sure, you can try to hide it under your pillow or something. I never lock up my belongings if I'm staying in a hostel dorm. Basically I keep all of my clothes in a duffel bag and keep my laptop, phone, passport, wallet, etc. in my smaller backpack which is always with me.

Nomad for nine years and never had any issues really. I had one iPhone 4 stolen about six years ago and another which went missing a few months ago -- both in Vietnam (Ho Chi Minh City and Danang), but both easily replaceable. Good luck and have fun :)