I also believe they are for the control boxes for the auto leveling system. At least they were VERY near them when I removed them (I was investigating the leak we had and trying to sort out the FW fill issue).
Yes, there are some other items down there that require access panels - there are accesses to electrical "J" boxes on some floorplans and the access to the Ground Control Leveling System "brain" is under there if the unit is equipped with it.