Hi,
While I'm waiting to get off these crutches (bad curb, bad curb), I went to the library and checked out some books on woodworkig and trailer design. One set of books is called Trailers, How to Design and Build by M.M. Smith. Volume one is Basics, Volume 2 and 3 are Strength and Towability. I checked out volume 1 and it appears to be well written with a lot of good photos and drawings.
Volume one covers design, suspension, brakes, wheels and tires, axle placement, electrical, safety devices, accessories (jacks, winches, tie-downs, anti-theft, etc), construction and an appendix of suppliers, manufacturers, reference, bibliography, and glossary of terms. I haven't had a chance to look at volumes 2 and 3 yet.
From what I have read so far, I'd recommend taking a look at Volume 1 if you, like me, don't have a lot of trailer experience. It would be good to look at if you are buying an existing trailer, too.
Kris