The spare motor thing is one thing I'm doing, too. Too cheap of insurance to pass up
Look on craigslist for a used kid's bike trailer. I got mine for $25. I'll be making a more suitable carrier portion from 1" x 1" square tubing and Mahogany plywood and parts from the trailer.
Your bike can pull more than it can carry and being in Texas it should be able to still climb any hills encountered....or are there any hills?