Ed,
If your generator is only putting out 27 volts, there is no quick and easy repair that can be made there. If you have a constant speed generator (10k or 12.5K), I do not know what is wrong other than it must be running at very low RPMs. However, if you have a variable speed generator (7.5K or 8K), the inverter in the generator or the control module is bad.
You will probably just need to run an extension cord from a neighbor's coach to keep your batteries up until the rally is over. I will be there on Tuesday morning, and I will be glad to run you a cord from my coach if we are parked close enough.
Gerald