By the picture you posted, it has both the side vents and the roof vent.  I do understand waht you are saying though.  I just installed a 6.0 Cu. ft. refrigerator in my trailer and installed 2 side vents.  I wasn't about to cut a hole in the roof of my trailer.  With that being said, I put the side vents in and was told by a local place that repairs RV refrigerators that it would be fine like that, and at the worst, may have to add an auxillary fan to move air over the condesor on the back of the refrigerator.  My unit cools fine, both on gas and electic without the added fan.  That is the case even in the extreme heat we have had this summer.

I would look more toward an obstruction of flow in the burner on the back of the unit. That is typically the cause of such a problem.

Pic attached is where i mounted my vents, and they work just fine.

http://i11.photobucket.com/albums/a197/sshep69/2012-07-19152511.jpg

You need to find a qualified service tech. If venting was the primary issue- it wouldn't work on AC or LP. The venting involves getting cold air in the bottom, and warm air cleanly out the top. If it is "broken", it affects everything. If it is working on AC, then the venting has been vindicated.

Yes- side in, and top output is preferred. But many units use side:side to good results. You appear to have a LP issue that has not been properly diagnosed yet.

Harmer builds a quality conversion, and I'm sure that an incorrect installation would have shown a venting deficiency, long before your acquisition of the trailer.

I would suggest openeing the bottom vent, where you will see the gas and electric supplies for your fridge. A common screw driver turning the fasteners 90 degrees, will open the top of the panel. If you follow the gas supply line to the bottom right of the unit, you will find a metal plate with a couple of screws. When they are removed, you will be looking at the burner section.

Any dirt, bugs or sagging insulation in this area will restrict a proper flame. A vacuum cleaner with a soft bristle brush will clean things ups a bit. Do not touch the very end of the burner where the flame is produced, with the brush. Blowing any residue off the orrifice is the best way to clean it.

While you are observing the area of the flame, have someone ignite the burner by turning on the fridge with the gas function. You should have a clean, regular blue flame, about an inch or inch and a half long. Within the flame, you will have a little probe that is constantly heated. If the flame is irregular and yellowish, or it keeps shutting off because the probe is not being heated, things can be adjusted to promote a good flame propagation.

The burner tip can be cleaned and the air flow regulated. The TC probe can be adjusted. These are simple fixes that only take a few minutes to diagnose and effect.

The amount of air being burnt during normal opperation is quite small. The surface area of  the two vents of your installation, would only be necessary to vent the gas fumes you might experience, in the event of a gas line failure where large amounts of vapours would be quickly produced.

You can easily trouble shoot this yourself, and anyone with any furnace experience, can make the adjustments you need if you can't do it yourself. A few minutes on the internet will show you how.

I don't think Camping World gave you the correct answer.