For what it's worth: outside of the ziploc bag trick, if I needed a bag that I was completely certain was waterproof, I'd spend twice as much on an Ortlieb pack (www.ortlieb.com). I bought one about 15yrs ago and still trust it.

But for carrying a laptop, a hard-shell pack is nice. I'm really curious to see what that XLMoto bag is like, especially at that price point.