i picked up 4 packaged bees last year for us and friends in our area. i drove ~2.5 hours 1 way to get them and bring them home.
the place i got them from in the Denver area was telling people to let their backhatch cracked (lots of subarus in CO) and crack from widows so there is airflow through the car.
if you can rig towels of something on the back windows to keep the car cooler, that would help too.
dont worry about a few bees getting out. the packages are sealed pretty good, but the place you pick the bees up from will likely have bees all over.
as i understand it, this is the time when the bees are the least aggressive. depending on how your packages were put together, the bees and queen have likely bee together less than a week when you them. they havent really formed a "hive" yet, so they dont have anything to defend (what i was told/overheard)
i have a few bees loose in the car - one landed on my on the side of my neck about 30 mins in and rode there all the way home.
installation tip* :
pull the cork out of the queen box and put in a marshmellow. hang up queen box in hive and dump bees [gently] in.
the bees will eat the marshmellow releasing the queen - but it gives you time to get the bees in, and the hive closed up before the queen is released. take queen box out next day
as mentioned above, you dont always need gear to install, though i wore it just in case
*this [we think] is partially what caused our bees to start to crosscomb in our top bar hive.