I have downloaded installers Rob, but when I re-build it will be fresh and direct into v4 with no v3 in sight (or ever having been installed, so no 'legacy' registry or file system hang overs either).
As time passes, more and more will be in this situation I think. A standalone installer that can 'unpack; a previously downloaded package would be useful in this scenario.
I can't recall what it was (nothing of yours, an aeroplane maybe), but I had to install P3Dv2 to get something installed and then moved to P3Dv3 with a lot of messing around to avoid version conflicts; I won't be doing that again; it either goes straight into v4 or it doesn't go in at all.
(...assuming I end up in v4 and not other, per other more recent posts)
PS "aeroplane" is marked by spell checker as incorrect! Fantastic ; on a flight sim forum too <GIGGLE>