Companys making/selling u-bolts will tell you that the bolts and nuts are different thread types (standard and rolled) so they self-lock when assembled. At the very least, don't re-use the nuts because repeated dis-assembly and re-assembly weakens them. It also stretches the u-bolts. True, nothing may happen... but one could also end up with a deuce with three rear axles that's extremely hard to steer.
Like welded steering components and re-using worn out brake drums "just 'til I can find a good deal on some better ones", some things shouldn't be done on the cheap. One could view "cheaper is better" as 'new u-bolts vs. the cost of a replacement truck'; not, new parts vs. using the old again. If your vehicle's value isn't worth the extra expense, how about the value of your hide?