The flat deck in use at my camp:
Here is a shot of the walking beam axles:
If you cruise through youtube you will see some pretty good trailers and can get some ideas from them.
My next trailer is going to have extra pieces in that I will have the ability to pull off my tub frame (or at least a part of it) and use the trailer as a log hauler, or use it as just a flat deck, or a tub trailer with a flat deck on top, and it will also have a fairly high canoe rack on it so that I can move longer materials (besides the canoe).
The possibilities are almost endless since I picked up my Lincoln PowerMig 255.