A/C Unit cooling some rooms, not others.

This is my first time posting here, and I have yet to see any other board with this particular type of problem on it, but there could be....

Anyway, I rent about a 30 year old trailer/mobile home with central heat and air....since it has started getting extremely warm/hot already this year, I've noticed something very hard to deal with, hard because I have to sleep during the day since I work midnights, anyway, the hard thing to deal with is that no matter how long the a/c runs, once you get to the back of the trailer it is as if a rollling heat wave hits you immediately....for instance on an afternoon where it is, let's say, 80 degrees outside, it's an easy 85/90 degrees in that room I would almost guarantee it...hard to deal with when you absolutely must sleep in there, one would barely not even want to STAND in there for more than a couple minutes, let alone SLEEP in there....yet if I get up and walk towards the living room, once I get to a certain point in the hallway, you are surrounded by cool air and the living room is very cool....

I had some trouble out of it earlier in the year due to stray cats getting under the trailer and tearing at the duct-work, at that point it was barely cooling ANYWHERE In the trailer and fixing that helped immensely...now it blows out air strong as possible (and cool air at that) in the living room kitchen and other bedroom, but when it comes to the bathroom and the back bedroom (right next to one another) it blows out strong yes, but warm....

Landlord says "not much I can do, I don't think there's a tear in it or a hole", so he says I should close off all the other vents and it will "make cooler air go to the back room, something I doubt, and as a matter of fact I've done that, and several other things such as that to try and get some cool air back there, to no avail....I still say there MUST be a tear, hole, or open spot on that duct work leading back to the room, but he says nope.

Does anyone here think I'm on the right track? Should I get under the trailer myself to try and PROVE that this is what the problem is, or could there be some other problem?