I use DE because it converts anything to anything.  I have no idea about the demo version or if they even offer it anymore.
Don't have Sketchup installed, but I'm sure there is a plugin to export OBJ.

On a fixer-upper, I take an OBJ into Lightwave, make an LWO out of it. From there, I can remap, add normals, or whatever.

There are plenty of free modelers that you can do that in.  Wings, Blender, Hexagon can do the fundamental operations you need for cleanup

And now I've got to get some sleep...I'm up way too late