I wouldn't use use muslin as a foundation fabric for a Dear Jane quilt. The blocks are so small with so many seams that I think the extra bulk would be a problem. I have used Paper solvy. I have heard of other people using a tear away water soluble stabilizer (don't know the name). With that they recommend removing the majority of it, and then the remaining bits wash away. I had bought a bolt of a supposedly disolvable stabilizer that I printed my quilting design on and quilted through. That was less than successful. It really did not disolve as well as the paper solvy.
However, I just found this link that might shed some light on the best choice to use.
http://www.generations-quilt-pattern...tabilizer.html