Sounds like screw cover. Yes you need it, it keeps water out of the screw rail so they don’t rust and let water leak into your trailer. It tucks into the rail and you can secure the ends. We use a color matched screw and silicone.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.