You have done the right thing and told the truth. No crime or assault should be changing your sense of values or ideals.
It is my personal opinion that your insurance company did not provide you with the tools under due diligence to even have one iota of a clue that they would not be covering your losses from theft. You were diligent in covering the items via case, (bag), and keeping said items in your locked car, and even on your own property within eyeshot and earshot of yourself and many neighbours.
How would anyone ever know they are not covered? In what year did insurance change and begin not covering items in your cab? What are people with hatchbacks supposed to do? Minivans have small trunks, cargo vans do not. Some pickup trucks have cabs behind, some have chrome locked tool cases, some people put things behind the seat. Windows up and locked doors have traditionally been enough.
Therefore how much expense has your insurance company ever incurred to educate you or anyone else about their newly invented weasel clauses. Were you provided with a DVD of what not to do? Did you ever get a VCR tape showing you common mistakes and misnomers that 99% of the population believes are so but are no longer so because of a microscopic line of fine print - that was not in your policy 15 years ago when you read it over - but now to everyones surprise is there.
You did not leave the items in a convertible with the top down for eight hours, so do not let your insurance company make you feel like you did.
You paid your money. You are and were insured. If they insist on shafting you - I guess you have to let it go, unless you can find an advocate. No use getting your blood pressure up or anything like that. I believe you have decided to not contest these people, but I just wanted you to know you have some backing here.