A lot of questions about insurance but would you really need to tell them? If it's that quick / easy to remove, couldn't you just take it out if you have an accident?
Always best to inform your insurer, even for non-performance upgrades as technically, these are also modifications and the insurer could void your cover when you need it most if you've not told them.
What would happen if (God forbid) you had quite a serious accident and couldn't get to the box to remove it before your insurer's claims engineer inspected the car? They could refuse to pay your claim on the basis of not declaring a modification, invalidate your policy, in which case you'd have been driving without insurance, which would bring all sorts of complications; getting a criminal record, cost of getting insurance in the future etc.
Not worth the hassle or the risk of not telling your insurer. If they want to charge too much to cover the performance upgrade, there are modification-friendly insurers out there so you could switch insurers.