A 12V DC shade motor we have been using has been damaged repeatedly by surges in current. The motor receives power from two wires and polarity is reversed to change direction of operation up and down. Many motors are operated by a multiplex switch and can move individually or collectively. Can a capacitor simply be placed in parallel to each motor to eliminate the damaging surges? I don't want to add resistors to the circuit because this system is in an RV so power consumption is tightly controlled.

You might want to check here:

Transtector System provides the best end-to-end power quality solutions to markets that rely on electronic equipment and communication links for strategic business functions, growth and stability. – Smiths Power (http://www.smithspower.com/brands/transtector/products/dc-surge-protection)

To narrow your selection of surge protector for your project there is a box on LH side. Choose the voltage there and it will only show that voltage intead of wading through everything.