SAUL of TAURSUS? Kidding.... Welcome to FGRV.
There's ALOT of unknowns here. Are you a welder? Certified? Not that you have to be certified but "knotty" (cold) welding can get you in trouble building a frame if you're not use to it. Most trailers...or at least my Scamp
which is very similar to the Boler
... is built from apx 1-1/2 x 3" steel tubing. Aluminum would be nice but that requires a whole 'nuther world of welding expertise!!
The cracks in the shell is more than likely a derivative of a broken frame. Of course fiberglass resin/cloth would be used to patch that...maybe just the fiberglass resin if it's not a "structural" issue where strength is concerned.
Dexter is a major manufacturer of axles. Dexter Axle - Trailer Axles and Running Gear Components - Home
I'm sure the entire axle
will have to be replaced. Question, do you know if it is a "torsion" axle
? (There wont be any springs under it.) I'm 90% certain it probably is.
Not trying to scare you or talk you out of it, just trying to give you a heads-up, but what you're tackling is NOT a small task!! Aesthetics is one thing, but road-worthiness with the axle, frame, body is another! And, if you're going to "contract" having the frame built, you'll have to consider some accelerating costs building it from scratch including installing and aligning the axle.