Just a note on size: I have a ~9" x 9" vent in my Boler
(the original Hehr vents in the Trilliums were also this size), and I started a thread about a month ago to see if there were any options for replacing that size except for the slightly cheesy looking Elixir ~9" vent. Beween my own searching and the ansers in th ethread, it seems that this is the only vent still made (RV type) in this size. (There are some marine hatches that are ~9" x 9" but they are a slighlly different animal - although they could be used.)
The point I'm winding up to is that you will most likely be enlarging the opening in your trailer and going for a 14" (or other sized) vent.
On the solar
topic, there are marine vents that have solar fans, but they are usually max of ~ 4" x 4". They don't lift open or let light
in, but just sit and whir to pass air in or out (your choice). Look for a "nicro solar vent" if you want to check one out.
Coming from a marine background, I was a bit surprised by the apparent flimsiness of all the vents, but then they are much cheaper (and often lighter) than the marine offerings. I did find one that looked to be of better quality - can't remember right now where it was, but it was a replacement vent for a Westfalia VW van. (maybe samba.com?)