I was going to make the same suggestion as Smitty. I know they've been used on some HDT fifth wheel haulers (essentially semi tractors with RV plates on them to pull really large fifth wheels). On a 1-ton (12,000 btu) unit you'll be right up against a Honda EU2000i's output; I'm not certain it would handle the starting load.
There's a Sanyo (and I'm sure more) that uses inverter technology to control the cooling so no starting loads as far as I can tell. It's here (and the EU2000i should just handle it):
http://www.minisplitsystems.com/cgi/dis ... num=12KS71
There is also Cruisair; which is like a boat A/C unit but air cooled. Here's a link:
Also I believe Sportyrick did a split install in his bus using (I think) a stardard window air unit as a base. You might look at his photo gallery.