I have the same panel on my Travel Supreme. It is a 5 watt solar panel to the chassis batteries. It is designed to keep a charge to your starting batteries when parked for a long time outside. It's OK but not 100%. I wired an outlet to my battery bay and have been using one of these for years.
Battery Float Charger, Automatic
I keep it connected all the time and never touch it. If I am plugged in, the chassis batteries always have a float charge. Not plugged in, the solar does help.
UPDATE, I just read that Entegra has a battery minder built in, I hope that is correct.