I just got off the phone with Fritz, one partner of RV Mobile, the link I gave in my first post.  Fritz and TK have more than 30 years each working on RV absorption reefers.  Fritz corrected me on the half bubble and said it is best, even with the new reefers and boiler systems, to use a round bubble level, placed in the middle of the freezer compartment floor, and get it as perfectly centered as possible.  I think his story of the customers who come in with a bad new-style cooling unit, due to operation out of level, and saying that they read that the unit can withstand it, quoting other RVrs, and even some manuals, says it all.  His very polite response?  "If that were true, why are you here with a bad cooling unit from Sodium Chromate sludge, or superheating of the outer boiler shell?" 

Hard to argue with that.

I am sure there are some that would continue to believe erroneous advice from their fellow RV “grapevine.”  I would imagine they could be called "repeat customers."

Fritz also gave me permission to quote several paragraphs from their website here.  Bold added by me.

Quote:

"Out of Level. If the cooling unit is operated in a stationary, out of level position (on any heat source), it will eventually become permanently damaged. Before we go any further, there is one more ingredient inside the cooling unit: sodium chromate. The ammonia solution inside the cooling unit is a mild corrosive, and sodium chromate is mixed with the ammonia solution (ammonia and water) to neutralize the corrosive effects of the solution, protecting the inner pipes of the cooling unit.

Since the cooling unit depends greatly on the effects of gravity for moving the liquids and gases inside, running it off level and stationary causes these liquids and gases to collect in unwanted areas and not be recycled back to the boiler. The liquid level inside the boiler begins to drop and become weaker. Eventually, the water in the ammonia solution begins to vaporize with the ammonia and leave the boiler. At some point, the boiler becomes dry and the temperature rises rapidly inside. The sodium chromate which was once in solution with the ammonia solution is left behind and begins to burn and permanently change state from a powder into a sort of sludge that will eventually plug the perk tube. If left to cook long enough, the sodium chromate will become as hard as steel. If the cooling unit were "saved" from this out of level condition by being leveled, or the heat source turned off, any sodium chromate that had changed state would not return to a powder in solution with the ammonia solution. This makes it possible to ruin a cooling unit a little at a time.

The new style boiler (see above) helps to prevent this cooking of the sodium chromate, but it can still happen. More often than not, however, the liquid inside the outer shell of the boiler vaporizes, causing the pipe that makes up the outer shell to become super heated and crack, thus ruining the cooling unit. [b]So, although the double boiler effect of the new style boiler may help prevent the perk tube from becoming plugged, it only gives the user a little more time to recognize and correct a problem. [/b]

When traveling down the road, the liquids and gases inside the cooling unit are sloshed around and don't collect in unwanted areas, making it all right to travel with the refrigerator on."

End Quote.

(reprinted by permission http://www.rvmobile.com

It would seem to be more hassle than it's worth to do that every time right?  What most of us do is to take a new, or new to us, RV to a fairly level place and then one time level it for the reefer perfectly.  Then we attach a bubble level with adhesive for side to side, and front to rear, near where our front power landing gear control is located. For example mine on my fiver is on the front left corner, so I have a front to rear level there on the side, and another level around the corner on the front that I can also see, that gives me side to side level.

I simply attached them (They have adhesive backs)showing perfect level when I did the reefer, and from then on use them as the reference.  Then it only takes a recheck every year or so.

On motorhomes with levels on the jack controls they can just note or mark where it needs to be for the reefer.

Hope that helps, and thanks Fritz for the correction.