I have a 16 watt RavPower solar charger myself, I don't have a trailer but I just strap mine with bungee cords to the holes in the charger opened on top of the tent on the rear bike rack.
I wasn't sure how well the solar thing would work but after using it several times I really like it, the only problem is lack of sun, so I bought a Anker 10,000 amp hour powerpack that is fully charged, so if there is no sun I just use the battery backup, I can charge both my iPhone and my two lights from that battery and still have 1/2 a battery left. When the sun is out I can recharge a 5% charged phone to 100% in 4 hours with the Nekteck, that's only an hour longer than the wall charger will take!
If you go with a solar don't go with anything less or more than a 16 watt unit, going less than 16 watts will take about twice as long to charge stuff, and while 21 watts is faster but you add another pound of weight, so you have to decide if you want to deal with the extra weight to get faster charging times or go for less weight and slower charging times. And you should get a backup battery, but I got a 10,000 one because it was only $14, but also the larger ones weigh quite a bit more, so I don't want the weight. Of course in case of emergency, you haven't had sun for a week, take your wall charger cords. But since I got the solar I've done several camping trips and haven't needed to use the backup battery.
Those powerpacks with a solar panel built on one side of the battery do not work well at all, I have a friend who bought one, and after a full day in the sun the powerpack battery wasn't even 1/4th charged! He sent it back. He found out later that you have to keep those charged fully off the wall and not to rely on the solar panel...well then why attach a solar panel to the powerpack? Anyway he ended up with something similar to what I got just a different brand, he paid more than I did but they both work just as good when we tested them. Anyway be careful buying these solar panel chargers because some do not get good reviews, one in particular costs 3 times as much as mine did and in tests I saw the one I got actually outperformed the expensive one.
The other think I do for tent lighting is using a Luci inflatable solar powered lantern, this thing is fantastic, I used it for 5 nights in a row and the darn charge level lights are still on full afterwards! And it casts enough light to read by easily. HOWEVER do not get the model that promises it can charge your phone, it can't, the solar panel is far too small to do that in a timely fashion, unless you allowed it 4 days to do it. The only battery powered light I have is a small Nebo Slim 400 lumen light that is very, well, slim, and it fits into the handlebar bag taking up next to nothing in space; because the one I have is not rechargeable I carry a set of AAA batteries in case the first set dies, but I don't use the light much, just rely on the Luci light; they don't make that AAA version anymore. I think the new rechargeable one would be great so then all you have to do is recharge it with the solar panel system.
Anyway, do your research before buying a solar unit, it has to fit for your needs, and the panels need to be the most efficient ones you can find, my research turned up the RavPower unit, your research could turn up something different.