HF Verticals... How close is too close?

[VK5TM]

If you can find a copy of NMEA 0400, there is information in there (it applies to boats and ships, but seeing as they are mostly metal, the info should be comparative to your situation).

Any chance of raising the vertical above the metalwork? Would probably mean using elevated radials though.

Otherwise, it's going to be a case of erecting it temporarily in various spots to ascertain the best operating point within that area.