Here's what I think: At the outset, the ability to buy a gun, particularly at a traditional gun-buying forum such as a gun show, certainly falls within the 2A self-defense right, albeit in a bit of a tangential way (after all, how do you vindicate your right to SD without the ability to buy a gun?).
1. The burden the county seeks to impose needs to be more precisely defined. The safe harbor they defined doesn't cut it. Nor should it in any way be the outer limit of what counts as "safe" storage.
1A. Whatever that burden is, based on what I've seen so far, does NOT amount to a direct burden on the fundamental right of self-defense (i.e. it is unlikely that copliance with this law will leave a victim unarmed in the event of a violent criminal attack). That means (in my world,
download the article here if you're interested) this measure should be subjected to intermediate scrutiny.
2. That burden needs to be supported by an "important" justification
2A. The health and safety justification will almost certainly meet this requirement, but we don't care so much about that, because we just want them to DEFINE what the justification is at this point. However, since this is intermediate scrutiny, the government DOES bear the burden of showing that their safety interest is justified. Sadly, I'm guessing most Cali judges would not require much of a showing for this, but if the plaintiffs were able to produce evidence that the safety problem complained of wasn't really a problem, the county could get tripped up here.
3. This justification must be "narrowly tailored" to meet the asserted justification in #2. This does NOT mean that the burden imposed in #1 needs to be the least burdensome way of vincidating that safety interest, but it certainly cannot be obviously more burdensome than some other method sufficient to vindicate the county's interest in keeping people safe--if they can even make that showing.
4. Ample alternative opportunity to vindicate SD right might well not come into play here. Also, no one argues that the government can't pass this law. It can. Whether it passes constitutional muster is another matter.
Ultimately, I think that under this framework, the county can probably impose some kind of "safe storage" requirement, but it can't be wishy washy and vague, nor can it require any old safe storage requirement it wants. That storage requirement will not be allowed to unduly burden firearms transactions at gun shows, and I think the "tethering" requirement is more burdensome than necessary to vindicate that government interest.
Hope that wasn't too long winded for you guys!