I am looking to install a second A/C in the front bedroom. Mine has no vent as well, just ceiling.
There are larger models in the Wildwood line that have the same dimensions, except longer length and a front A/C comes with those.
Try looking at the trailers in your line and see if they have the front A/C from the factory.
There are videos on youtube showing installation of A/C where no hole existed. Looks like some wood bracing is required to create a box between the horizontal roof beams. Other than that, seems straight forward.
With just a fan, you could probably just tie into 12v from the ceiling light.
I would need to run a dedicated separate 20 amp service to an extra A/C as my camper is only 30 amp.