I wish I had better news for you -- but fixing a front cap leak, on any trailer, is a big job. You'll have to peel back the front and the roof till you see undamaged studs. And it sounds like the leak went pretty far back -- all the way to the slide? Or maybe that is a separate leak.
In any event, this is not a great job for newbies, unless you are an experienced woodworker or metalworker. You will have to replace the damaged studs and then will have to patch the roof and re-fiberglass the front cap.
The good news is that there are plenty of DIY how-to videos on youtube, so you can teach yourself how to do the job right. Do you have a covered place where you can work on the trailer during the winter?
Good luck. I sure hope I am wrong about the magnitude of the tasks ahead of you.
2012 Fun Finder X-139 "Boondock Style" (axle-flipped and extra insulation)
2013 Toyota Tacoma Off-Road (semi-beefy tires and components)