Found this in the wikis [not tested it myself]

http://docs.xfce.org/xfce/xfce4-panel/theming

Add this to ~/.gtkrc-2.0.

style "xfce-panel-window-style"
{
  # Time in miliseconds before the panel will unhide on an enter event
  XfcePanelWindow::popup-delay = 225
 
  # Time in miliseconds before the panel will hide on a leave event
  XfcePanelWindow::popdown-delay = 350
 
  # Size of autohide window in pixels
  XfcePanelWindow::autohide-size = 3
}
class "XfcePanelWindow" style "xfce-panel-window-style"

Thanks.  That does the trick . . . after logging out and in again.

http://docs.xfce.org/xfce/xfce4-panel/theming

Add this to ~/.gtkrc-2.0.

style "xfce-panel-window-style"
{
  # Time in miliseconds before the panel will unhide on an enter event
  XfcePanelWindow::popup-delay = 225
 
  # Time in miliseconds before the panel will hide on a leave event
  XfcePanelWindow::popdown-delay = 350
 
  # Size of autohide window in pixels
  XfcePanelWindow::autohide-size = 3
}
class "XfcePanelWindow" style "xfce-panel-window-style"

As for the hiding problem itself, you can minimize the number of pixels shown by changing the value to 1. (I don't think zero works.)

Then set a background image that has a gradient that shifts to black so that when the panel hides only a single row of black pixels is visible.

HTH

Set the opacity to zero on the 'Leave' slider under 'Appearance' in panel preferences.

I tried that but the old nVidia card couldn't handle HWA so had to turn it off in Window Manager Tweaks.  I also tried to install the nvidia-kernel-legacy-96xx driver but I couldn't get it to work (even though it worked fine about 5 years ago).    Besides a transparent BG made it harder to see the icons.

Any suggestions on the timeout issue?

I do wish that there was a time adjustment to keep the panel visible a bit longer.  Gnome panels have this feature.  Is there a way to add it?

Is it possible to autohide panels completely? Currently it hides and there's a strip of pixels remaining so you know where your panel is, but is there a place where you can setup this strip to be gone/smaller/bigger? Im not interested in seeing the strip cause I know where the panel is.

Can the tolerance also be set in seconds needed of your mouse to raise the autohidden panel?

Most (if not all?) desktops have this strip when autohiding panels... But if you still see it, it's not yet hidden

Thanks!