You might find that your estimate is a little optimistic. I doubt you would get 20 mpg out of a conversion van. I have been advised by many, during my search for a vehicle, to think more like 12 - 15 mpg. And if you then plan to put luggage on top - altering the aerodynamics of the vehicle - you would need to drop that even further.
The only other question I have is, if you do not have the necessary funds to pay for even a cheap motel for the two of you, how are you going to fund an unexpected breakdown? No matter how well the vehicle has been maintained and checked over, it can happen. It happened to me, in Alaska. Three days and $800 for the repairs, before I was on the road again. Meanwhile I had to pay for taxis, accommodation, etc. That was in a well maintained vehicle, completely checked over before departure and only 55000 on the clock.
From your first post....
What sort of work, and where? From what we are hearing down here, work is not exactly plentiful at the moment, in your country. It may not be something on which you want to rely.I've been wanting to travel the road for a few years now and I'm finally getting my chance, only problem is, I won't really be working except for the occasional job along the way ...
As for finally getting the chance.... you might like to note that I was a senior citizen before I ever hit the road in the US. Now, a decade and almost 100000 miles later, I am planning my fifth trip. Why not work and save till you can do it without financial concerns. You may still choose to sleep in your vehicle - as do I - but it will at least be worry free, knowing there is a fund to cover any and all emergencies.
Lifey