Ok, do it this way.
Go through 1st grommet on passenger side, carrying the main wiring loom. Cut carefully above the loomand use a little oil to ease the cable through.
now it gets fiddly as you have to go past pollen filter and through the big grommet into the cabin.
In order to remove this you should remove the glove box for improved access.
Once you have cut though that grommet, feed the wire through completely. Now before you replace the grommets, make sure your wire is the right length in the engine bay (and has a fuse no more than 6 inches from the battery).
If it is then you want to use a little bathroom sealant on the grommets before refitting.
That is the hardest part done. Then it is simply, remove kick strips down the passenger side, feed wire underneath and replace.
Getting into the boot is quite straightforward.
Be aware though, a standard 5m power cable only just reaches the boot area. You wiuld need to mount a splitter for the power cable right in the corner.