You just need to know the distance from front to back of your trailer. If the expandable sections are longer than your hitch to bumper, I would assume you need to know that number to insure you fit in the site available.
For the record, I've never needed to know total length of my tow rig and trailer unless I am going in to a pull through site for the night and planning not to unhook. All other times, I just need the length of the trailer only.
Oh, and welcome to the forum.
2017 Jay Feather 7 22BHM Baja/Andersen WD
2018 F150 4x4 3.5L Ecoboost Max Tow
2015 MB Sprinter 2500 Passenger 2.1L Diesel
2007 Ram 2500 4x4 Cummins 5.9L G56