Fridge usage in class B

Our normal routine. 48 hours before we leave refer on. 24 hours before load food. Day of, depart.
But we also leave our trailer plugged in 24/7 at home.

I turn it on a day or so before I'm planning to leave. Unless you are planning to leave food in the fridge, I'm not sure why you would want to leave it on all the time. I don't think there is a negative impact by turning it on and off.

You can do it either way provided you store the RV in a spot that is level when not in use. I don't know of any real "downside" of either method since there are no moving parts in the fridge. I've had some RVs that the fridge ran all during the summer and others that I turn off and on only when needed. My CURRENT fridge I turn off when not in use and the reason is that it takes only about four hours to get completely cold. Some models can take as much as 24 hours and that would be a good argument for leaving them run (if you tend to be a bit spontaneous as I have been). Never wanted to delay a trip while waiting for the fridge to cool :)

We use our van about every weekend. I generally run the fridge on gas and turn it on when we get going. I put stuff in the freezer as that gets cold pretty fast. Then I move it down once the fridge cools off. If I'm bringing a lot of stuff, I cool it down the day before. I think it is better to use it than not - particularly the gas feature. You do not want things building up in the piping - such as spider webs.

If I had the RT in the driveway, I'd fire it up a couple days before a trip, not just to pre-chill it, but in case there is an issue, you can possibly get it fixed before you have to head out with a dead fridge. There are many full-timers using these fridges 24/7/365.25, and because the only moving part is the liquid, it can't hurt to keep it going. My preference is to run it on propane, but one can go either way.

Of course, this is assuming the fridge is on a level stretch. RV absorption fridges will self destruct (and the damage is cumulative) if left on and out of plumb for any real length of time.

We plug it in 24 hours before departure and load it just before we drive off. Turn it off again when we unload upon return. We do a lot of 3-4 day weekenders at the moment.

We fire it up a couple of days before we leave on a trip. Put stuff in the second day and leave the next morning. That way, all the opening and shutting the door is done and everything can get to a good nominal temp.

We always plug in when we do this because we also want our batteries to have a good 48 hours to be absolutely charged. Then, we run on 12vdc going down the road and then on propane when we get where we are going (most of the time, because we boondock). I check the refrig on propane every few months year round just to make sure it is operating correctly.

Operating RV absorption refrigerators off level is what causes failures.
Damage from operating off level is accumulative....a little damage (clogging) each time until tube failure due to inadequate flow.

Turn it ON and let it run
OR
Turn it ON/OFF as needed (ON day before trip for cool down)

Just as long as it is level when running.....on electric or propane

A local rebuilder told me absorbtion fridges will last longer if they are left on. The temp swings of turning it off and on cause the tubing to stress and crack sooner.

I would recommend switching it between electric and gas every so often. Two reasons: It keeps the bugs in the flue guessing, and if you find that one of the burners is out, you have time to get it fixed.