If the tank was full and uncontaminated in the first place, there really is no easy way to get it contaminated with fungus just by sitting around. A shot of Redline, Power Service, or Stanadyne Premium fuel additive wouldn't be a bad idea in case any condensation occurred.

__________________
1982 300DT 190K (Diesel Purge + synthetic oil=smoothness at last!!!)
2004 Ford E-350 6.0 L PSD 227K
2006 Dodge Ram 3500 SRW HO Cummins 4X4 48RE 42K (brute force tow vehicle)
2005 Scion xB wife's rolling pop can
1993 GMC Sierra C3500 6.2 142K