Its a nice little trailer
I somehow missed that your trailer had a window on the side and a vent up near the roof.

which is why I was pushing the roof vent like it was all important.

Your set for ventilation , with your head at the floor vent end you would probably get fresh air to breath , which is always nice.

Good idea, copper pipe idea should work like a mini hrv. Just remember the slower the air moves the more time it will have to warm up.