My question is: Why the hell would you fly VFR on top?
If you're VFR on top the only way to navigate is dead reconing. I don't think many pilots will be succesfull navigate 300nm without propper verification. Ok, you can use your radio instruments, but they are not mandatory in VFR certified a/c.
If you realy want to fly above the clouds, get an IR. It is that easy.