I would seriously advise against a seen through quilt. They are very difficult compared to any baffled design. A top quilt done in the same fashion as the UQ you made will work perfectly fine. Since a 40 degree quilt is relatively thin, I would recommend the Karo step method to reduce the amount of baffle required. It's not easier not harder in my opinion.
Here's a link to my 40 degree quilt the I made in the Karo step style. It's 1.6" thick and keeps me nice and warm at 40 degrees.
And here's a picture of the finished quilt. There are other pictures of it under construction in my gallery.