Sounds like a fun thing to do but if you're hauling a bike trailer full of gear no doubt you will use almost twice the battery power. Having some solar panels to help keep a spare battery charged sounds like an interesting strategy. E-bike batteries have quite a large capacity so you would need a solar array big enough to supply enough juice if you really want to be able to charge such a large battery. That said I'm not sure it would be worth trying if the array ends up taking up a lot of space, is weight prohibitive or simply can't produce enough current to charge the battery in a reasonable amount of time. ( I'm no expert on solar arrays so someone else with more experience in such things needs to add their two cents ).
Years ago when I was still strong enough I wanted to try bike camping with my mountain bike. I had a particular place in mind but in order to reach it I had to pedal my MTB up a long 2.5 mile long forest road and then along a about a quarter mile section of rocky single track to a very nice little mountain lake. I did this with all my gear packed inside a backpack. Sure was hard as hell pedaling with all that weight on my back but somehow I managed. The pay-off was I had that whole lake to myself once the sun set and that was really cool. Years later I wanted to do it again but didn't think I had the stamina since I had gained weight which would of made it so much harder.
Now if I convert my MTB to e-assist that might once again make such excursions possible again. Of course if I did that I'm going to want a kit with a motor strong enough to help pull the extra load ( 750-1000 watt ). Plus I'd likely buy a small single wheel trailer to hold the gear ( no way I'd put that stuff on my back again...lol ). Just thinking of doing that again is enough to inspire me to convert my MTB over to e-assist. Of course if I did that I'd likely need to run the motor at the 50% assist level ( or more ) which of course lowers your mileage range. How well this would work would depend on how far I would have to ride and the number / length of the climbs I would need to ride. Puts a grin on my face just to think about it.