I need to seal cracks in front top of trailer

I really appreciate all these suggestions.
Will do research on each, thanks

Just want to also mention, the skin is fiberglass. I know the comment about Bondo means well but not certain that is a proper product to use on fiberglass... unless you know it is. I have been surfing all of my life, yes I now live in CO, but point is I've done a lot of fiberglass/resin work and to keep things waterproof, make sure the proper materials are being used. The only problem I see with repairing the current cracks is the waveiness from the previous leaking will never go away unless it is replaced... and that includes using Eternabond.

I actually have used this to fill in a hole in my exterior fiberglass skin Sun Cure 4.4 Oz. Fiberfill Repair Kit and it works great. This will not separate from the fiberglass skin and will be permanent. I do keep a tube of this in my TT. When it cures, it is more opaque and it will need to be sanded to be smooth but it is great stuff for fiberglass.

If you do the repair, non-replacement style repair, you could always get a sheet of diamondplate, form it with a curve and attach it to the top to cover everything up. With an added new metal seal on the bottom and using the existing metal seal at the top along with new dicor, it may end up looking OEM.

If you find total replacement to be a bit pricey, you might be able to get some 1/16th inch thick fiberglass sheeting. It will be able to be pulled down to follow the curvature. Use a good, waterproof construction adhesive. Have someone help you, start and the top, get it all squared up and start working it down around the curve, gluing and screwing it down.

If you down it carefully and find some auto trim strips, or something to hide the edges, people won't even notice the repair. Folks only notice when it is not done carefully and is obvious.

We are starting to get a stress crack in ours. If it goes any further, I will use this technique to fix ours.

Here is an idea that "might" work. Sand the entire front cap smooth, then apply a skim coat of "bondo" ( bodyfiller, you can buy it at any auto parts house ), then sand that smooth and paint it. How "good" of a paint job you apply would be determined by how perfect it needs to look ( or how, "less than perfect you would accept" ). You could do it all in an afternoon.
This is going to sound funny, but honestly, you could likely get a coat of paint on there that would be acceptable with a roller.

Thanks, will check it out.

For aesthetics, I would look into replacing that entire front exterior section. It probably would not be too difficult but definitely do your research first.

If you are not too concerned about looks, the widest Eternabond you can buy, starting at the lowest point of the damage, and then layering horizontal strips, like roofing, would work. Just make sure to clean the surface first per the recommended instructions. My only concern with Eternabond is how well it would do with items, bugs, rocks, etc. striking the surface there. Eternabond is a very good product though.