Add padding around edges of table.

gt <- gtable(unit(1, "null"), unit(1, "null"))
gt <- gtable_add_grob(gt, rectGrob(gp = gpar(fill = "black")), 1, 1)

plot(gt)

plot(cbind(gt, gt))

plot(rbind(gt, gt))

pad <- gtable_add_padding(gt, unit(1, "cm"))
plot(pad)

plot(cbind(pad, pad))

plot(rbind(pad, pad))