Yes. The fridge
should be sealed from the cabin, as running on propane
produces carbon monoxide.
But won't you run the fridge in transit? If so, the vents should be left uncovered. Both lower vents are for the fridge, BTW. The bottom is the access panel for the controls and the top is the exhaust (for heat and combustion gasses when running on propane).
If you turn the fridge off (and use blocks of ice to keep food cool in transit), you could cover the inside of the vents with pieces of plastic (assuming they're removable). I've heard folks who take their trailers to Burning Man have to take measures like that due to blowing dust in the Mojave Desert.
If the vents are riveted, you could use a rectangle of vinyl with snaps on the corners, maybe Velcro along the sides. That's what Casita
does for their A/C vents on models that don't have roof A/C.
For the stove vent you could just tape the flap closed, no?