All GIMP 2.x have the same system path. The only difference is the user folder where there is gimp-2.8.
Here is a guide on how to compile MathMap:
viewtopic.php?f=9&t=4550but not easy work.
It should work with the .deb package from .rpm.
You may want to uninstall and clean again everything related to MathMap and do what "rich2005" comments in the first link. Manually copying the MathMap binary (making sure it is executable) and expressions where they should go in your user folder ("/home/YOUR_USER/.gimp-2.8/plug-ins/" and "/home/YOUR_USER/.gimp-2.8/mathmap/expressions/".
Also you see the message from "adam933" about dependencies. But I think those two packages are required by the .deb package, so they should be installed.