Absolutely stellar observation and information here.
The very best thing to do with these batteries after removing the shrink wrap is to wrap them up with some polyimide (Kapton) tape.
This stuff is legendary. When you look at a mars rover, this is the golden stuff wrapping up nearly every component on it. It holds up under incredible stresses of all kinds. Super high temp, super high voltage, etc. For example, a dielectric strength of ~8,000 volts per mil. It also stays put at 500* F.
The best source I know of is here (Hopefully this link is okay?)
1 Mil Tape (Polyimide) - 25.4mm X 32.9m
I live right near them and could do a group buy discount if you want to avoid shipping and individual cost. That said, they beat everyone already even per roll. I have no affiliation with them what-so-ever, but I was tickled to find an amazing source of this material. I use it for just about everything.
While I don't -yet- have a Mk1 insight, I would never build or rebuild a battery pack of any sort without this stuff. I mostly deal with LiPo batts too. Those can be REAL picky little buggers.
I hope this is helpful information, and thanks for all that you guys do as a community. Lets keep these amazing vehicles on the road!