I own a 71 nova currently and live in southern california.  My car has minor rust issues but overall is an extremely good project car, however, it does have some problems that need to be addressed.

It rained heavily last night and this morning I opened the trunk and the two doors to air out the car.  My major concern right now is the rust that has been forming in the trunk.  Because of weather stripping that has seen better days the trunk floor is getting a good amount of surface rust, especially in the railing indents on the floor.  My plan is to replace the weatherstripping in both doors and in the trunk (that should stop the leaking to the trunk pan), but I want to repair the damage in the trunk that has occured.  The rust isn't nearly bad enough to warrant replacing the pan.  I came accross an article in CHP that talked about using POR-15, has anyone had any experience with this stuff and has it been good/bad?  I also want to do this to my floor pans because at one time they were rusted and have been fixed by the previous owner, but some spots are thin where the por15 kit has the reinforcing material that hardens when it is put with the paint to fix it.  My biggest issue doing this myself is I have had no experience doing body work, could this be undertaken by myself or with a friend?

My other question is this thing has a sunroof (I didn't put it in and I want to put a new roof in and fix this once I take autobody at school in the future).  There was some moisture this morning after the rain where the 6x9 speakers are on the passenger side.  The only places I can see it coming from are the rear window not being correctly sealed, or the sunroof.  I want to say the sunroof is unlikely because during rain while driving the car I have never noticed the hoodliner become wet and no dripping has occured on the inside where the sunroof is.  If it is the rear window that is leaking and not the sunroof then just getting a rear window gasket from goodmark should fix that correct?

Any help is extremely appreciated!  I don't want to dive in head first and do something that is going to take more time to fix if i mess up.  On the other hand, this rust needs to be repaired after I fix the weatherstripping and I need to find the other source of the leak if I'm ever to put in a stereo system.  I'm not an electrical expert but I know having moisture up by your 6x9's in the back isn't a good thing and could cause alot of problems if not a fire.

the rear glass is simply held in with adhesive. chances are that there might be rust at the lower edge of the glass and you should take a look around there to see if there are any holes visible. if not, then there might just be a leak around the window. if you take the glass out, the stuff you need to reseal the glass is pretty cheap. there is an adhesive that comes in a roll made by 3M that is meant for that. its called Window Weld Ribbon Sealer or something like that (PN's 08610, 08611 or 08612 - the different #s are just different sizes). you would lay down an adhesive primer first, then lay that ribbon down. then pop the glass back on. its not that hard, but dealing with the old adhesive is messy.

ive been using POR-15 in my Galaxie which was pretty crusty and from what i have seen so far, it seems to be working well. the places i have applied it have had no more rust break through, even though i have had break through happen again in one untreated area. i took care of that again and put some POR-15 there to stop it. so far so good. POR-15 is cheap enough that i would use it even as a preventative measure. they sure arent kidding though about the 'only time will remove it' part if it dries on your skin. im not sure where you are in SoCal but Classic Industries in Huntington Beach keeps it in stock and its about $35 a quart.

i actually work at an auto paint store out here in SoCal too, so if you have any other questions ill do what i can to answer.

The first thing you need to do is to figure out where the moisture is coming in - I'm betting on the window seal or rust perforation.  I believe that yours is sealed with what is called butyl tape (dum-dum) - it is black and VERY sticky.  You need to remove the interior and exterior trim get a hose and some paper towels and see if you can find the leak(s).  You say that the rust is minor - check to see if the are any paint bubbles around the suspect areas.  If there are, I'm betting that you have a hole in the sheetmetal and this is where your water is coming from.  Chevys had a problem with this in the 1970s.  If you don't see bubbles in the paint it is probably a problem with the seal.  This is easier to fix.  Either fix the leak by inserting some butyl tape in the leak or remove the window and reseal the entire window (be VERY careful you don't break the window).  There are special tools that look like a handle with a knife blade at a right angle on one end and a piece of cable on a handle to pull it with. If you are not comfortable with the removal option try the other.  You can sometimes soften the old bytyl tape with laquer thinner to get it to stick to the new stuff.  

As to the trunk - I would try and get a new seal a soon as possible to stop any further damage.  I have not used POR-15 but Car Craft has said good things about it.  If the rust is not heavy and flaky you can probably just sand the rusted areas down and paint them.  Watch rustoleum paint as it does not tolerate gasoline at all.  

Good luck and don't be afraid to ask questions here.