I hear LeadNav is replacing many Lowrance units in race cars now.
I do not Apple so Backcountry is the next best thing, from the research I have seen.
From Leadnav, seems all you have to do is open them to get them into leadnav...
GPX files can be simply imported by clicking on them and choosing to "open in" LEADNAV. This can be done through Safari, Email, DropBox or they can be Airdropped back and fourth between devices.
You can also hook your device up to a computer running iTunes and just simply drag them into the apps Document folder.
Please take the time to view the Quick Guide as page 10 covers this
leadnavsystems.com/resources/Tutorial-Docs/LeadNav-GPS-Quick-Guide-v3-Sept-15-Low.pdf
Also the first minute in video 1
leadnavsystems.com/support/videos/Support_videos.html
If need be converting GPX, KML, KMZ, USR back in fourth is covered right here on the forum
forum.leadnavsystems.com/discussion/89/converting-file-types#latest