I noted some concerns about moisture and mounting the vertical upside-down.
Looking at the instructions it does appear that this could be a problem,
both from the feed point and the radiators.
There is a drain hole right above the matching network that says "Do Not
Cover", which indicates that drain hole is needed. If mounted inverted a
new drain hole will need to be drilled probably at the end of each
element so water does not become trapped at those junctions. Drain
holes need to be large enough to be effective and small enough to keep
critters out. http://www.rogerhalstead.com/ham_files/AV-640/AV640.htm
See third row of photos from the top.
In addition the bottom of the antenna is a tube and this area would
likely need to be weatherproofed as well if for not other reason that to
prevent water from accumulating and freezing which does happen all the
way into Florida and the Northern gulf.
Operation wise side mounting will affect the pattern but no more than it
TowerTalk mailing list