There's really nothing scary about the frame rust in those pictures. It takes a long time to actually weaken the frame. You will rot through the body parts much sooner. Still, rust is inherently hideous.
I get my cars sprayed with this thick grease every year or two. I don't know what it's called, but it coats your tools, hands, everything as you work on the vehicle - very sticky! There is a local shop that does it for about $200 and then the "touch ups" are only like $30. They recommend this every 3 years, but mudholes and dust have a way of wicking the stuff off much faster.
If you can find somebody who does this, you won't even have to knock off the existing rust - unless it is really loose. It slows the rusting a lot because air and water are no longer getting to the metal. It moves around a little on hot summer days and it doesn't seem able to trap water underneath it.