couldn't help myself with that last post..
real answer: you probably don't need anything.
yes, there are occasions where fire destroys things. every day safety features prevent the majority of this stuff.
assuming your collection is in the $15,000 or so range, yes that's a lot of money. but for reference, over on the DB forum that amount would get you a "nice student instrument" or something like that. you'd be shocked at how many $20K+ basses just get placed in a corner of an apartment in brooklyn - and never see a problem.
I remember in college a violinist i knew had a really fine violin, priced over $50k. it amazed me how she just treated it the way i would treat my $3,000 bass. not reckless, but it just got used, like it was anything else. She was a top-notch player and was working all the time.
the idea of investing in something over the top like that to keep your basses safe is like a healthy person wearing diapers every day "just incase." just take care of your basses, buy insurance if that gives you peace of mind, and keep on rockin'.