I think that synthesizing down all the issues that impede long-term boondocking, the show-stopper constraint for us is:
black water capacity. For us, this is appx 7 days "out", before one has to run back to "civilization" with tail between legs....to dump the black water tank.
So, the second biggest constraint for long term boondocking, is the food cooling situation. Given the above black water constraint, we need to have cooling for up to 7 days. We can achieve this with our large "Extreme cooler" at $25 CAD, which can
easily take us 7 days. Overstock food that needs cooling goes in there (the cooler is kept out of the baking-hot truck cab and in the shade), and we use the ice and ice packs in our 3-way fridge for every-day next-in-line meals. We don't want to open our Extreme cooler till our 3-way fridge stock is depleted. No need to even turn on the 3-way fridge propane. However, it is there if we need it (a break-down way out in middle of nowhere). Also, we transfer some ice from the Extreme cooler into the 3-way fridge at about day 4 (around 1st line food depletion date).
Now, the next constraint is water: our toilet (the largest porta-potti on the market; with an AA battery pack flush system); PLENTY of water in the fresh-water side to do us 7 days. We also carry some jerry cans of water for dish-washing: plenty for 7 days boondocking (no need to run the 12V water pump). We have a D-cell electric shower for an outside shower, if need be (drawing from our dish-washing water reserve). We carry drinking water gallons for drinking (more than enough for 7 days).
....by this point, we haven't used nary 0.1 amp-hours of battery power....
OK...now, we need light at night: both outside and inside camper, we have LED lighting (I keep 1 incandescent bulb for ambiance lighting...used rarely). We need only 1 or 2 LED lights at night for reading....for max 1.5 hours. Our cell phones and hand-held radios get charged with a portable lithium power-pack if need be (good for 7 days at least). We have smart-phone music (plug in the head-phones). We never use the roof-top power vent....even when it was 107 in the desert (we sit in the shade outside under the awning; and at night the desert gets quite cool).
....by this point, our house AGM Group 27s are barely used (!). So, we may splurge, and charge a laptop from the house system. Still, nearly nothing used in the house 12V storage. So, between the truck batteries (we have 2 of those) and everything, we're drowning in excess 12V capacity....at 7 days. No solar. We can re-charge the house system as we drive at the finish of the 7-day period to empty the toilet black water (and, empty our 12 gallon portable gray water tank, too).
So, so far, solar would be a real luxury; something fun to tool around with for fun. I would only get a panel that I could move around (with small light-weight balsa-wood stand) to keep perfectly aligned with the sun very few hours, and toss it under the dinette seat cushions when we move...
On edit:
I was also getting by fine with my 2 group 24's. That was until I recently added an inverter to run the coffee maker. Of course we got by for years using other methods but I like the convenience of my baby keurig.
...we just boil water, and pour it into our 1.2 liter bodum (French press), and we have a huge quantity of coffee...no electrics needed :D