This rig has spent it's whole live in the PNW so corrosion isn't really an issue. There's hardly a spot of rust on it.

Point taken about just topping it off. Thing is I just topped it off a couple days ago and checked it yesterday under similar conditions and it seems like it's dropped pressure by about 10 psi. However, the pressure seems to fluctuate a bit each time the compressor kicks on. Could just be the cheap gauge but sometimes it dropped to about 15psi and other times it was up around 25 psi. The low reading just made me think that maybe it's losing refrigerant at a rate that's going to require topping it off every couple weeks. It could be that when I filled it I just didn't put enough in though. We're going to be moving to Texas in a couple months and I was just trying to be proactive in case I need to get it repaired.

I'm just going to sit on it for a while to see if it does drop to nothing again, but I was just curious about the best way to check for leaks in the meantime. It doesn't seem to be leaking anywhere in the engine bay though.

BTW, I have been checking for leaks with a black light/yellow goggle set.