I think it was in the town of HÖFN. It was built for a viking movie.

We rented their smallest camper. It had a foam mattress on the floor, a sheet, and a light blanket. There is no insulation or heater in the small van. My GF and I brought our 30 degree (0 Celsius) sleeping bags and I was perfectly comfortable. It got below freezing one night, and hovered above freezing most of the other nights. My GF gets cold easily so she needed the van turned on so the heater could run; right before bed and to wake up in the morning. The other issue is with condensation from breathing all night. Bring a small pack towel to wipe off the water on the inside walls and ceilings in the morning. The next model up offers a heater option, but you should reserve those months in advance. Personally, I don't think a heater is necessary in September if you have adequate sleeping bags... Unless you or a loved one gets cold easily.

That's really helpful, thank you very much :)

Panasonic G9

It's possible, but the sky is often too cloudy. The day before we flew in the lights were really good and even visible in Reykjavik. Most of our trip was cloudy and rainy.