First of all - do not freak out. And ignore all posts saying to avoid Chicago area, it’s just BS. We are not a gun nazist in Illinois. 
Second - I’d more worried about checking your luggage during departure, not upon arrival in Chicago. However, what can happen in Chicago.. your luggage may be lost, especially at O’Hare Airport.
So, first advice - use any tracking tag inside your bag.
Third - do not use TSA approved gun / ammo cases or locks. The only person who get access inside those cases is you and nobody else. These cases must be opened with you present. Any hard shell gun case with locks (or loopholes for padlocks) is ok.
Fourth - inside the case: use the cable lock, put it through the magwell; keep the slide locked to the rear. Magazines are unloaded. Ammo packed in original boxes. (check details of airline’s rules). Make it as safe looking as possible. (especially for screening)
Fifth - check the rules posted on airlines website. TSA is only 50% of things you need to know. Each airline may have their own rules (thank God, mostly these are the same between airlines, amount of ammo may vary)
Sixth - give yourself extra time for processing at destination airport. I’m guessing your luggage with gun case will land on baggage claim carousel… and this is a nightmare at O’Hare. Sometimes it may take over 1 hr to get it.
Seventh - know your rights (print the rules on remember where to find them), your knowledge must be better than TSA or airline’s personnel knowledge. If they don’t know something, ask for manager.
Regarding you trip back to Florida - this is super simple. Illinois allows non-residents with valid out-of-State permit to carry their firearm within the vehicle while traveling through the Illinois. No need to lock or disassemble your firearm. I recommend avoiding speeding - you never know how knowledgeable the Officer will be and once, he figures out you carry, your traffic stop expands from 20 minutes to 2 hr. 
So - be knowledgeable and smart. Make everything easy and even look more safe than is should be. This way you do not need to worry about anything.
Good luck !
