[R] Adding plane in a 3D scatterplot

[Megh Dal]

I have drawn a 3D scatter plot :

library(mnormt)
library(scatterplot3d)
dat = cbind(rmnorm(3, rep(0,2), diag(2)), 1:3)
scatterplot3d(dat)

Now I want to do 2 things :

1 : In the Z-axis (i.e. height), I want to see only numbers 1,2,3, etc NOT, 1,1.5,2,2.5.............

2. I want to add two Horizontal planes at hight z=2 and z=3. Those two planes should look like "bottom" of that 3D plot [i.e. like Grid-lines].I already gone through "$plane3d" but could not get through. In the help page, a description is given with a regression line, however I could not understand how I can implement that in my problem. 

Any help will be highly appreciate. 

Regards,