Securing my laptop inside the Prius v

I purchased this envelope from Amazon:
Amazon.com: Pacsafe Luggage Travelsafe 12L Climbing Pack, Black, One Size: Clothing

I store my laptop there and slide the envelope inside the laptop compartment in my backpack. Then I tie it to one if the metal loops in the trunk, close the cargo cover and I feel relatively safe against a robbery. I say relatively, because anybody with the proper size wrench or an adjustable wrench can remove the bolt tying it and take the backpack.

I wonder if any of the experts here knows the size of those bolts, and were I can order a security replacement bolt. I'm also open to other ideas on a more secure way to tie this bag. I have tied to the frame of the seats, but there the backpack is visible from outside. I prefer it to stay hidden.

 

Still, I would prefer to replace the bolt by a security one. However, I don't know how to specify the bolt size/type if I intend to buy it in Internet (the local bolt/nuts store that visited does not carry them).

 

Keeping it with me have worked almost always, except three times when I left my backpack behind (JC Penny, Subway and Ponderosa) . Not that I stop on my route home every day, but only three incidents in about 18 years is a very good record, don't you think? Still, the laptop is heavy and I look for the freedom of not carrying anything when stopping to buy something or when taking the kids to the Judo class after picking them at their school. Going home to leave the laptop is not a feasible alternative in any of those cases.

Currently I hide my backpack under the cargo cover (is this walk you call tourneau? Sorry, not good with French here.

 

Junkies around here break you car window to find something to sell to get $5-$20 to buy their fix. While your laptop might not get them $20, they certainly should get $5 or $10. No thanks. The window glass is too expensive for that method.

My current method buy me some time, but if I give them enough time they could get a wrench and do the job before I return to my car.

 

Yeap, I love the cover.

 

I spend a lot of time out of my desk, with little time to plug the laptop in, so I use an ultra capacity (read big) secondary battery with my company-provided HP Elitebook.

HP 12-cell Ultra-capacity Battery with Adapter (EJ092UT) specifications - HP Small & Medium Business products


It last the whole day.