I don't totally understand the theory of operation: Just how wobbly are they
supposed to be? Mine have a hub that's maybe 1/8 inch thick and they have
about two inches of axle to ride around on laterally between the stops. Is
that normal or might I be missing some bushings or something? It's a 20
year-old ShoreLand'r trailer.

"Gene Kearns" wrote
If I correctly understand your description

A picture is worth a dozen words:
http://blizzard.zmm.com/images/wobblies.jpg

As you can see, I overestimated the length of axle over which the roller can
travel. It's more like one inch. (I was half right...) The rollers can
achieve full wobulation within half that distance, and they really don't
need to wobble anywhere near that much to conform to my bottom, so I'm
thinking while I have it apart for rust removal, I might add addtional
spacers to make the rollers roll a little more smoothly. The spacer that you
can see on the right in the picture appears to be a piece of 1" galvanized
electrical conduit, by the way.

"Gene Kearns" wrote
I'm thinking wire brush and/or sand/bead blasting and some cold
galvanizing spray, too..... especially if you are in salt water..

Strictly fresh water here. I got an estimate of $900 for a complete
sandblast and paint job, which is probably fairly reasonable, except that I
don't have a spare $900 lying around. I've been working on it a little at a
time with an angle grinder and wire wheel, followed by ospho, red oxide
primer, and an enamel topcoat. So far I have one roller truck finished.
(That estimate looks better all the time...)