rectGrob(gp=gpar(fill=NA,col=NA)),

Plot Footer

my_g1 <- grobTree(rectGrob(gp=gpar(fill="#F0F0F0",col=NA)),
linesGrob(unit(c(.05, .95), "npc"), unit(1, "npc"),
gp = gpar(col = 'lightgrey', lwd = 4)),
textGrob(" medavis6",x=0,hjust=0,gp=gpar(col="darkorange",fontsize=8,fontface="bold")),
textGrob("Source: R",x=.85,hjust=-1.06,gp=gpar(col="black",fontsize=8)))

Plot All Together

allplot <- grid.arrange(my_g2,plot20,my_g1,heights=c(1.17,11,0.5))
grid.draw(allplot)