I didn't give the size or weight of the battery pack because I didn't realize it would affect much, but you may well be right that the hole tapping/threading/whatever method might be different depending on the weight. The battery pack weighs right about 10lbs. The weight would be distributed between three holes over a distance of ~28cm/11in.
Here is a link to the battery.
http://www.pswpower.com/ven.php?cargo.2018-1e-rg6c
Using all zip ties is no good. A thief would have it off in all of 1/2 second. I would have to cut and replace the zip ties every time I wanted to remove the battery and charge it. It would just look ugly and janky.
Using a zip tie at the one end does solve most of those problems, but not quite. If nothing else, I'd still go through ~30 zip ties per month. I'd feel ****ty putting that much plastic in the land fill.