You could use red diesel legally for your generator if you have a diesel generator if it's mainly used on private property. Just not in the tank your bus is tied to, unless your bus is only for your property and never expected to drive anywhere.
The 1200 watts isn't needed or used on PC's with PSU's capable of that. Only if you are doing like 3D Mark at highest benchtest settings are you ever going to come close to it and even then you likely won't draw that much even with the most powerful cards. I'd spec for 800 watts as you could hit that for testing builds. When PC's, even gaming ones are idle or just running Windows or Linux but not gaming, you'll be in the 100-300 watt range, and it won't ramp up and use it unless you start gaming. So for repair purposes, you only need to run simple 3D apps to know if it's working or not.