I have a 2008 Chevy Uplander and one of the codes that came up on the computer is p0449 which has to do with emissions. Also, I noticed when I fill the gas tank up, I get a huge wet spot up in between the drivers seat and the pedals. It isnt gas and has no overbearing smell at all. Is this moisture and does it have something to do with the emission codes?

SOURCE: emission code 0455

code CODE PO455 fuel tank large leak.replace it .dont cost much.if that not it you have a evaporative leak.

SOURCE: 2003 Mazda MPV trouble codes

check the pcv hose at the back of the intake manifold it often leaks and will cause several idle problems

SOURCE: emission system

you have a code in the emission system comp telling you you have a fault, you will need to have the codes read by volvo

SOURCE: P0449 Evaporative Emission Control System Vent

While looking for the location of the vent/solenoid for you, I came across a blog that said this error can be caused by a loose or faulty gas cap. You may want to look at that first and possibly solving the problem. Replace the cap, get autoparts store to reset the code and see what happens.

SOURCE: The check engine light on my Chevy Silverado cam

That is laymans terms. That is why it is in your manual. You ,need to get up to speed ,on todays somewhat high tech vehicles.
Now you need to go to a shop that does EVAP testing, with a smoke machine,if necessary,or at least put a scanner on it ,and replace the vent valve solenoid,if bad.(again laymans part teminology,