Don't know the Night temps but Having been a Boy Scout--(And ex Marine but that came later)- I used to make a Bivouac out of a Groundsheet and used a Bivvy bag- Basically a plastic bag to sleep in. Only a few years ago - I did a trip with no tent- A bivvy bag and a tracksuit for night warmth. Far better when we found a barn to sleep in but If you do go lightweight- Do not forget the extra night sweaters.