I've always been an advocate for bringing more batteries rather then a solar charging setup. I know plenty like the solar chargers, but I found it to be much more efficient to get a bunch of high capacity battery banks and charge them at home then to have to worry and fuss over a Solar panel all day.
My first trip down the ditch I had a Goal Zero solar panel and two medium sized battery banks. Everything I need to charge on a river trip is USB based (phone for listening to music and taking pictures and tablet for reading and multimedia use), so this worked fine for the first week until I had depleted the power banks.
I was using the Solar panel a little bit to try and save the battery banks, but found them to be very finicky. They aren't water proof, so you have to constantly be taking them in and out of dry storage. Even during the flat stretches you gotta make sure they are in direct sunlight, so frequent adjustment is needed. I also found that it was sensitive to high heat and would stop charging once it got hot which is pretty crazy for something designed to require direct sunlight. Its also useless in obvious times like sunless days and at night. At least with that Goal Zero 7 charger, it didn't fully provide the needed amperage to charge stuff unless it was in direct sunlight and but not so direct that it overheated the solar panel.
So essentially the only time it was able to be used reliably and easily was the few hours between getting to camp and sunset and I just didn't find that to be sufficient and ended up doing what many advocate for by just leaving it all in a dry box and enjoying the canyon on its own. I try to do that anyways, but I'll admit its nice to listen to tunes or watch a movie before bed and I find it makes the experience better not worse for me.
Before my second time down the Canyon, this last February/March for a 23 day trip, due to my negative experience with my solar charger, I decided to purchase three 27000mah battery power banks. I calculated that these would more then sufficiently charge my phone, tablet, bluetooth speaker and a gopro without ever needing to get a solar charger out. It was super nice to be able to just plug them in and go do other stuff without having to babysit them. I could plug it in overnight and wake up to a charged device. I ended up not even needing the third battery bank and basically always had charged devices. I found a great deal on the power banks, so it ended up costing me about the same as a decent 21w Solar Charger.
So yeah, I recommend really looking at whether a Solar Charging solution is really needed. At least with what is available currently, the complication and cost of a solar solution isn't worth it and I'd rather just bring extra battery capacity.
I think one great solution that I've been wanting to try is the Nissan Leaf battery modules. They are slim and compact, lightweight, easy to put in series, have lugs to wire them up with, come in a robust weather and shock resistant housing and aren't horribly expensive for the capacity they provide.
A few of those modules in an ammo can, a decent volatage regulator and a decent charge controller at home and you'll have a robust, lightweight and efficient high capacity charging solution.