You will be fine.... just do not get in a hurry when parking/backing up and if you have an urge to...slow down. If you are the least bit unsure with anything, even when you have a 'spotter', get out of the tow vehicle and do a 'walk around' to survey the area.
As for the '24 foot length, that is usually measured from the "back stop" of the unit parking space to the 'street'. From where your wheels are positioned, 6-8 feet of you unit will go 'beyond' the 'back stop', to give you not 24 feet, but around 30-32 feet.
2013 Forest River Salem Hemisphere SBT312QBUD
2001 CrewCab F-250 7.3 PowerStroke Diesel
SuperChip, BTS transmission, 6.0 Trans Cooler