Fridge on propane is not a huge draw unless it is really hot outside. What you will find is that using cooler bags with ice packs is a really good way to transport food outside of the fridge. What we do is fill our cooler bags and use ice packs at home then transport the bags either on the floor or on a bed closer to the back of the trailer. You will find that keeping the trailer balanced in load can be a little tricky. Many times you do not want to load center or forward. We try to keep the forward weight down a little because we have 2 batteries on the hitch and that loads the trailer front heavy if no consideration is taken to distribute the load inside the trailer for transit.
Your pickup is more than adequate for your purposes but leveling air shocks or air bags do make a difference and can help compensate and level a tow rig without having to put too much torque forward on a WD hitch.
Our tow suv has a self leveling air suspension and it really helps level up the tow profile if used with a WD hitch. But one needs to shut the engine off when parked on an uphill slope with the trailer attached because otherwise the self leveling function can make hitching up a royal PITA by adjusting the level of the SUV when you do not want it to! Unfortunately there is no defeat switch for the system so it just automagically decides that it is going to inflate the air bags without your consent. LOL
Our Sierra 1500 pickup just has springs with regular shocks so we need to put a little more pressure forward with the WD hitch to set the tow profile nicely.
2 twenty pound tanks is more than enough for a week during summer and if you have over 160 amp hours of batteries you should get at least 3 days during cold camping and up to 5 during the summer when the heat is not really needed.
Dry camping off grid the main concern is holding tank capacity and conservation of water. Toilet usage is the big ticket as is using too much water to do dishes. IMO this is a good exercise in teaching children just exactly how much water we all tend to use and the fact that we take if for granted and are in the habit of using far too much here in the west.
Don't get too upset if you find that it is not your children who are using the most water
I speak from experience on this issue and sometimes I have become a little bit too overbearing with someone who does use far too much water without thinking about it..
But don't start a war about it, just tell the person who filled the grey water and black water tank that they will have to use the public facilities and or fetch more water rather than hooking up the trailer and doing a dump and pump after only 2 days off grid.
You will find that using freezer packs to travel will also give you the advantage of being able to cool the fridge faster when you do park the rig. It is not a good idea to run a fridge going down the road contrary to popular belief it is far better to use ice packs for that purpose because compressors can and do fault out when not level. Our dometic fridge does not tolerate more than 3 degrees off level without causing the unit to shut down rather than causing compressor damage.
Some fridges are designed to work on 12 volts while the unit is in motion but others are not so you will need to check to see if being off level can cause issues with your unit. I have only fault coded our fridge once and fortunately the protection circuit worked and the unit was not damaged but it did need to be shut down and have the trailer parked on a level spot for about an hour before it would start back up again.
30 gallons US, which is our fresh holding capacity lasts my wife and I about 4 days if we are careful but we also bring our cooking and drinking water separately from the holding tank in the trailer or we use the park water systems which are all tested and chlorinated here in BC and the potable water in all BC provincial parks must meet health standards and is perfectly safe to drink and cook with. Same with the National Parks.
Next year I will be rigging up a second power supply to use instead of a generator. Personally I find generators to be a PITA and not worth the noise and effort. The second power supply I have in mind is two 200 amp hour 6 volts rigged up in a case in the back of our pickup truck with it on wheels so that it can be easily rigged up as a backup or off grid extension so that we can camp for well over a week at a time without using a generator at all.
We do run our dvd player and TV and changed the less power efficient tv that the trailer came with to one that only requires 16 watts. So all I use is a cheap lighter plug type 12vdc to 120vac 80 watt to run the tv off grid. Our older system does not include an inverter but has a cig lighter plugin above the TV. We only have about 160 amp hours of battery capacity at present but it does give us good service for at least 3 days if we are careful.
Even watching a few DVDs and or TV we still get 4 days of battery during summer with no heater running at night. We never use the 12 function of the fridge and always run it on propane though because the 12 volt system on the fridge would run the batteries down very fast indeed the propane system on the fridge uses almost no electricity and not that much propane especially if the fridge is pre cooled with ice packs.
I would imagine with children it might be a very good idea to use coolers for beverages, or if you have guests that hit the beer supplies hard then the use of coolers will definitely extend the propane supply and keep the food cold.
We also turn the water heater off when not in use either during the day and especially at night so we do stretch our propane more than most people.