Are you asking about charters or the Ragbrai baggage service?  Some differences, mainly size, but yes, they are very reliable.  I’ve always gone with a charter, not the Ragbrai baggage service, which is included in your registration fee.  The number of bags on the semis can be quite large, so finding your bag can be a challenge, but with unique markings, not too bad.  To get the bags from town to town, just throw it on the truck in the morning and it magically appears at the end town in the afternoon, unloaded and stacked in rows.
Check back here over the next year and you’ll learn “everything you need to know…..”; plus, a little more.

btw–a lawn chair and change in clothing at each town is overkill.  Remember you are on a camping trip so wear clothes for several days.  Personally, I bring old undies and t-shirts, wear them for a couple of evenings, then clean the bike with it (t-shirt, not underwear) and toss in the garbage.  Keeps dirty clothes to a minimum.