The easiest solution would be to install several of the computer type fans on the inside of the lower vent, using nylon ties. That's what I did. I used five fans and connected all of them to a switch. I had a twelve volt bar to draw power off along with a ground, so for me that was an easy choice. You may have a similar bar on the lower left. It is black with wires connected. Good luck.
Obviously, fans on top are more efficient and would be the first choice, but as you indicated access is the problem with that option. You could always have the frig pulled out later at a RV repair facility back in the states later.
