That really depends on how much junk was in that trunk. A child's body would fit in something as small as a suitcase or large backpack.
The bag of trash may have been right in front and since it had active maggot activity it was immediately tossed for the "ew" factor. There could have been another bag at the back.
Two things strike me...
Could Caylee have been in that trunk, with the smell worsening, but hidden in or behind something the tow guy did not see? Could George have done something with Caylee's body in the backyard trying to conceal it during that mysterious time he was home but wasn't home and the car was clean but wasn't cleaned? What were George's actions and moves in the next 24 hours?
I am not saying George did these things. I am asking if it is possible, not probable.
Also, the LE said the trash bag didn't smell like the car. That does not make sense if the trash was in the trunk the entire time the smell was worsening - it should have picked up odor as well as leaving it. Why does this bother me?