I've used POR-15 on a car chassis before (frame-off restoration of a muscle car). It's great stuff and not too hard to use but be warned it is messy and does not wash off. Wear clothes you don't mind getting trashed. Wear rubber gloves (it won't even wash off of skin). Put down a drop cloth. Don't expect to clean your brush either, but the cheap foam brushes from Home Depot work pretty good.
If you need to re-seal the can, clean out the lip as best as possible and put some plastic wrap in-between lid and can if you ever want to get it open again.