Need to adjust the legend size and title position in tmap package of R?

Question

I have produced the maps of spatRaster layers as shown in the top image. I want to increase the width of the legend by stretching it a bit longer horizontally (it should have a size similar/close to the combined size of the top three panels), so that the legend text representing rainfall values shows clearly with some space between the values. I also want to put the title of the legend on the left side of the legend.

Check out the bottom image that I scanned to get a good hint of the legend form I want to get.

I have used the code below to produce the maps.

tm_shape(stack) +
    tm_raster(style = 'cont',
              n=10, 
             palette= get_brewer_pal("RdYlBu", n=10, plot=FALSE),
             title="Rainfall (mm)",
             legend.is.portrait = FALSE) +
    tm_shape(muda) + 
    tm_borders("black", lwd = 1)  +
    tm_layout(legend.outside = TRUE,
              legend.stack = "horizontal",
              legend.outside.position = "bottom",
              legend.outside.size = 0.1, 
              legend.text.size = 1,
              legend.title.size=1.5,
              panel.labels = c("NN","IDW2", "IDW3", 'OK', "KED"))

Any ideas and suggestions please?