Congrats on the rig and your first successful outing!!
Yep, slide-outs are mucho awesome! I really dig mine.
As with the previous posters regarding the fridge. A/C or Gas (gas/battery combo). 3-way use to be the norm but no longer as running on just battery as opposed to A/C or gas/battery combo used up your batteries mass quick. They still make the 3-way though. Ammonia absorption refrigerators work on the principle of heating the ammonia to create a high pressure situation and as it evaporates it “absorbs” heat thereby cooling the inside of the fridge. Overly simplistic explanation but the general principle. For a better job of explaining than I can do go here http://www.nh3tech.org/abs.html
There are 2 main brands of fridges used in RVs, Dometic and Norcold.
The Dometics generally have an on/off button and a gas button, an auto light and a check light. The temperature on most Dometics is automatically controlled. When the gas button is in the “out” position it will operate on gas only. With the gas button in the “in” position it will operate in the auto function (plugged into shore power it will run off of A/C, no shore power it will run off of gas). Now, when it runs on gas you still need a good battery as the battery is what sparks the flame on and controls all the electronics. Dead battery, no fridge. With the gas button in the auto light should be lit, with the gas button out the auto light will be off. The check light will flash while either in the gas or auto mode (while running on gas) if gas is not getting to the fridge. This happens with an empty tank, tank off, or air in the lines. A quick fix for the air in the lines is to light up your stove to purge the air as it is usually close to the fridge. Once it gets lit you have gas pretty close to the fridge.
The Norcold brand of fridges work the same way as the Dometic with the exception that most of them will have a temp control switch as well.
Also on some of either fridges depending on model there may be a “frost control” switch. This is for use is humid climates and is basically a mini heater to keep them from frosting up around the freezer door.
You stated that you have a “have a DSI electric water heater “. DSI stands for Direct Spark Ignition. There will be a switch (probably with a red lamp next to it) somewhere in the kitchen. Flip the switch, lamp comes on gas fires up, hot water (as with the fridge you still need the battery to control ignition and the controller board). BUT you stated yours was DSI electric. The electric part means it will also run on 110A/C. If you do not have a switch on the inside (my old one did, my new one doesn’t) of your RV for turning on the A/C part of the heater, go outside and open up the inspection panel and look for a small toggle switch usually on the lower left-hand side of the water heater. Flip the switch and it will then be running on A/C and no need to turn on the gas although gas heats the water quicker. Just remember to TURN OFF the switch as part of your packing up because if you plug back into shore power for storage the heater will be on and will boil out all of the water and ruin the heater.
As far as driving with the propane on.......... Check your local laws on that one. If it's a short trip (less than 4 hours) I'll leave mine off. Longer trips with a fridge full, I'll turn the gas on.
Ok, long post. I’m done.