I have a camper van in Iceland for 10 days in September. Should I travel the ring road or spend in-depth time in 3-4 different areas??
Here's my honest take: do a modified Ring Road, not the full loop at breakneck pace, but a shaped version that lets you linger where it matters most.
Either way. Ten days is the minimum, IME, for the ring road, and that is good if the weather cooperates. Early September tends to have better weather than later, but starting in September the weather can change quite drastically and you lose daylight . Plus most campsites close by the middle of the month. There are some that are open, but you would need to plan ahead and for those that are open you would want to double check that showers etc are available. That is not always the case as some stay open as far as a place to park and camp, but no amenities.
If this were my trip, I would not do the ring road and instead would do the south coast, golden circle and Snaefellsness. That way you can see things without being rushed.