1995 E-150 u-joints or rear bearings?

I have been to 4 mechanics and talked to a few. There is a lot of noise coming from the back of my van. When I first start out in the morning, it is OK. About 20 minutes on the highway and it starts to make noise. The longer I go, the louder the noise. This has been 4 months now. This week it has started vibrating with the noise. I feel like I am riding a vibrator, it's in the stearing wheel, foot pedals, seat, etc. If I keep it under 60mph, it doesn't get to the vibrating part, but the noise is still there,however, not as loud. The noise is the loudest the faster I go and the longer I go. I travel 27miles a day to work one way. Yesterday, a guy said he thought it was the u-joints and said that if they freeze on the highway, my van will flip. Other mechanics have said it's the bearings. What do I need to do? Is it safe to drive? Which is the problem? U-joints are cheaper than the bearings. If I replace the u-joints will that work? Money is tight. P.S. It has 208,000 miles and I have replaced the engine, transmission, brakes, front end and various other things like the radiator, etc. Thanks for your help.