I do the same thing as Weight except the cord is for satellite Internet. I, too, would totally thread a cord or install an inlet in a vent. It's a good idea. You need to have a hole somewhere; why not use an existing one?
Is this vent on your trailer at the typical right rear lower corner?
If so, its a bit farther to run a shore cord to the typical RV power pedestals at most campgrounds. But if you aren't planning any of that, and simply want to plug in a generator, it will work fine.
On my trailer, I replaced that plastic vent cover with a 3" cord inlet with a small sliding door. I use it as an inlet for coaxial cable for antennas. (my trailer is a comm-trailer for ham radio, so I need to be able run cables out thru access ports).
I also drilled a 3" hole in the wood floor, and installed a cord inlet, at the front left corner, for shore power and additional cable entry.
It’s awfully convenient since my battery box is going to be right there too. Just worried about the integrity of the vent after cutting into it. Easily replaced though.