Thats where you (and many others ) are wrong ....Tom just has proven that hooking-up is essential.
Everyone can perfect do without hook-up lead / hooking up at sites IF you drive every day or each two days .
But the batterys need to be charged on 220v for a 24h cyclus once in a while (each month would be ideal)
Driving/alternator does not complete this cyclus even if you drive 1000km a day .
You will do fine without hooking it up but it does bring down the lifetime of the battery.(Tom has proven this even having a solar panel )
If Tom had a hook-up lead when he took of at the start of his trip and he plugged it in each time when he was at a site that provided hook-up in the price (witch many sites do) he had not flattend his batterys , i think two times now .
The price of the lead could saved him the trouble he had when his batterys where dead , and saved him buying a new battery for his Cali after only one year(witch he probally wil need now to be sure ) , and using a 220v kettle a shorter wait for his tea in the morning
Fully flatten a battery is never good and again shortens the lifetime everytime you fully flatten it.
Even with solarpanels the batterys need to be topped-up on hook-up to keep them in the best posible condition.
Everyone uses his Cali he think is best , but some things need serious concideration and charging the batterys on 220v is a essential thing to do.
So back ON topic , what do you all need to buy for your Cali today (if you do not allready have it ) .....a hook-up cable like Tom just did.