There is no way a "Slight Change' will make it work. To make it work the two legs have to be 100% independent.
Now what you can do is convert your rig to a single Air Conditioner type.. (Well, sort of) to do this you do make a "Slight Change" basically you remove the wires that feed ONE of the air conditioners from a junction box or the breaker box (Exactly where depends on the rig) put a "pigtail outlet" in place of the wires you removed at the junction (NOTE: this may be a many foot long pigtail) and put a plug on the end of the wires you removed. Now,,, On a 30 amp site, you pull the plug and use an indepenedent extension cord to the 20 amp oulet.
There used to be a web site, last few times I tried it there was no joy www.PSRV.net
Check it out.