I had something similar happen to mine, only it was caused by a tire blow-out. I did my best to fix the dented area and spray painted the affected area to match the existing color. it's still dented a little, but it was a lot easier than replacing it. I have no intentions of EVER trading this trailer. It's the last one I'll ever own.
Now, if the J-channel is actually torn, you could pop-rivet a new sheet of aluminum behind it, smooth out the J-channel and repaint the scratched paint. I suppose it's just how much you want to spend and your ability to fix things like this.
Another option is to turn it over to your insurance, take a hit on your deductible, and have a shop fix it.
2019 Montana High Country 375FL Fifth Wheel
2014 Chevy Duramax HD 6.6 - 3500 Diesel Dully Long bed Crew Cab