I was thinking that perhaps one of those "unit specific upgrades" caused the Hauler that you upgraded to fly. I would say it should be a cheap upgrade though, and the other option would probably be some sort of impressive speed increase.
The unit cannon idea is an interesting one, and could still be just as useful for it as an air unit...
My current idea, since the main base makes its own power, is to set a town hall someplace that leaves room for the harvester, then build the harvester in the power field, then make your workers to grab the gas.
Or, hell, if the idea is still going through with? Add a power structure to cover the gysers and build a couple automated harvesters.
Congradulations, you just cleaned an expansion with one worker.