If you can get behind the crack in the fiberglass nose piece, you can probably restore that part pretty well. First, you need to be able to grind out an area all around the crack from the back side
through any paint or insulation. Say 6" minimum all around. Bridge the cracked area with three or four layers of cloth or matt and resin. Once that's set up, you can grind out the crack from the outside. Assuming everything is dry, I'd try to seal the ragged ground edge of the crack with resin. Once everything is cured any body filler will do fine. Use primer and a finish filler like "Green Stuff" if you want a nice job. I'm assuming you don't want to fiddle with gel coat so you'll need to finish off with paint. You would need to do this to any other area where the fiberglass has been cracked.
Not sure what's going on with the puttied areas across the top. If there is an overlap between the sheetmetal and the fiberglass end cap, these two might be riveted together to close up what looks like a major gap. That could be a problem area, closing up that gap. After that, consider removing all the "goop" and run a nice clean bead of butyl caulk along that joint. Be careful with this stuff. It is tenacious and sticks to anything, especially your finger if you try to smooth a sloppy job. Then you have stuff stringing all over .... well, try it, you'll get my drift.
This area is the one that's tricky and I've got to go with Donna and Roger here. Added to everything said is the structural flexing across the damaged area. Bondo has practially no mechanical strength, JB Weld is better but this is a flex area. There's pretty much no way to avoid using rivets here. If you're willing to go to some trouble, this variation on Roger's idea should achieve what you want.
First cut off any crimped or bent edges around the hole. Find a decent thickness of sheet aluminum that is as thick or slightly thicker than the rest of the trailer. Flashing, as found in the hardware store isn't thick enough. If you can't buy a scrap from a local fabricator, try an aluminum cookie sheet. Form it as accurately as possible to the curve, from the inside, and an inch or so larger than than the hole. Clean the inside skin all around the hole a couple of inches. Now, (don't laugh), use some J-B Weld to glue this patch over the hole from the inside. Let it set up for a few hours while you go back to the hardware store.
Nowadays, when we say "rivet", we mostly think of pop rivets. When my Dad said rivet, he meant a small little aluminum or brass gizmo that looked like a flathead screw without a slot or threads. Find some aluminum ones, 1/8" shank size. If you've done a good job in forming the patch to the curve, 3/16" long should be enough. Get a countersink, the flatter the angle, the better. From the outside, drill 1/8" holes 1/2" apart all around the perimeter of the hole. The J-B holds everything in place and bridges any small gaps between the patch and the skin. Next, carefully
countersink each hole from the outside just barely so the taper goes through the skin, not the patch. Have a helper go inside, de-burr a hole, stick a rivet through, then hold a hammer to the back of the rivet. Now, using a small hammer from the outside, gently tap the end of the rivet flat into the counter sunk hole. (Think "Airstream") It probably won't go perfectly flush. If not, you can partially level it off later with a file and sandpaper then feather your filler out a ways to blend it in. Don't worry about pretty, just be throrough. Do this for every hole. When done, you'll have a patch that's secured well mechanically to the skin and as near to flush as it's possible to get. Now
you can level out the hole with body filler, sand smooth, finish off, etc. etc.
(I just reread Donna's post. I haven't any experience with marine epoxy but it sounds like as good or better than J-B. Give that a try if you don't have J-B.)
All of the repairs, above, are using well supported materials with the same expansion properties as the base material.
Best of luck!