Hopefully not having any living quarters in the van will keep costs down.
Right up front, there is no DC-DC transformer. Period. You would use an inverter to get AC, transform it to the desired voltage, and then rectify that back to DC. Simplist would be to use the high voltage DC directly. 90 volt DC motor controls are usually used from 120 AC power. A good combination there~~~
That said, would you consider an "old school" cab-over camper? The forward bunk space will serve as an air dam outside. You would get the stand-up space needed, if for nothing more than stretching, which will be needed, trust me. Not using it as a bunk opens up a lot of generic space, although I would be careful of the weight forward.
A 3/4 ton pickup is a given with a diesel, and a good idea for a camper anyway. I have had both a Ford and a Chev 3/4 ton with king cab and a short bed. The combination worked to keep overall length down. I don't know what sort of camper shell could be found that would fit that combination though. Normal usage would be a straight cab pick-up with an 8 foot bed and a cab over rig. I'm sort of partial to King Cabs for traveling. A lot would depend on your milage driven.
Batteries inside living/working space is a bad move. Although I am biased, having been burned with that situation. Burned literally, with the acidic smoke getting into my lungs. Made a hell of an impact on my income stream as I transitioned from working as a mill electrician to a fiber optics splicer.
There are several considerations for space for your work and other that only you can make. But I stand on my comments about using a small 120 volt generator with an externally accessable enclosure. Keep the CO outside and avoid using the propulsion engine for extended power usage.
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Anything that looks residential (like someone might be sleeping in it) would cause me problems in my neighborhood.
My city might have the worst homeless problem in the whole country. People seeing RVs and campers parked on the street sets them off.
We have a lot of that here in Santa Cruz as well, everything from meth-heads living in clapped out vans to high-end Sprinter type rigs with rich folks inside. People have a right to be concerned about their neighborhood becoming a campground, apparently Santa Rosa doesn't even let your park a camper on your own property either.
Vehicles | Santa Rosa, CA
Read more about regulations concerning auto dismantling, campers, RVs, and more.www.srcity.org
So, if you did want a camper you would have to pay for storage. I have my trailer stored in Nevada where it's cheap $45/mo but I'd be pretty angry if my city restricted what kind of legally registered vehicle I could have on my property.
I did live in a truck camper for about a year twenty years ago and I was able to find parking where I didn't get hassled. Most towns now have ordinances though which prohibit sleeping in vehicles on the street.
This is something that we need to deal with as a society since so many folks were already living on the edge before the virus eliminated so many jobs.
So, we have officially strayed off-topic but now I understand why it's so difficult for you to come up with a good solution. Maybe this summer just try running a Sherline lathe in your motel room, plastic makes a great material to practice with and the chips won't hurt your feet if some go astray.
John