What I do that seems to keep it from skinning over is when i go to use it i never open the can,, that's a big mistake if you ask me... I just drill 2 1/8th" holes in the lid at opposite sides,,, one for pouring and the othe for air, when i'm done i put self tapping screws in the top.. I've never had a problem this way when going to reuse, and the only way I ever buy it is in the gallons, when you need to reuse if you can't get the screws out, simply drill more..lol
I like there stuff for the most part, it is impossible to get off of skin though, Por patch is nice, as far as rust prevention goes, seems to be ok, better than most other things, but I usuallly try to make things pretty darn clean before i use por15, leaving rust on something doesn't seem right to me.. lol... I like using it on door bottoms when doing door bottom repairs as it's hard to get ever angle clean,,, i'll put POR 15 on so that way it can run in the crevices, then POR patch after POR 15 is dry,, seems to work good. Used their header paint on the triumph i've restored, haven't seen it peel off yet, but it probably doesn't have 20hrs on it yet,, hopefully it doesn't do anything stupid.. argh..

Anyways over all I really like their stuff, and can't seem to find anything that does the same job better, but nothing ever seems to be perfect.

one more thing when you brush it on it seems to level itself out rather nicely...

hope all this helps.