1) you have the names of the checkboxs set to be dynamic:
name="<?php echo $row_rsTours['trID']; ?>-VolunteerPosition"
this wont work, the checkbox names need to be static.
2) in the insert record behavior, bind the column you wish to store the checked values to the checkboxes.
3) after making the binding change, add  to the end of the checkbox names
4) add the code i provided at line 1.