Thanks. I got this to work.
I had alway thought that the "." would restore the original AutoCAD defaults.
(setenv "PrinterConfigDir" (strcat (getvar "ROAMABLEROOTPREFIX") "\\plotters"))
(setenv "PrinterDescDir" (strcat (getvar "ROAMABLEROOTPREFIX") "\\PMP Files"))
(setenv "PrinterStyleSheetDir" (strcat (getvar "ROAMABLEROOTPREFIX") "\\Plot Styles"))