I am thinking of sewing up two separate fleece sleeping bags, that when combined will be one large sleeping bag for a couple. I am looking into the option because it's cheap and I think it might be effective. If I use a 200-300wt wind resistant fleece, what temperature range should I expect the fleece sleeping bag to go down to with two people inside?

I am thinking about using such a system with my girlfriend on the Superior Hiking Trail from late May to late August. We would be using closed-cell foam pads held together with pad straps. What temperature rating should I expect? Weight? Any other things to think about?

Thanks in advance!