> Any suggestions?  

Although automotive relays are rated for low V and high I, they
will switch a lot of wattage, 300W or more. The problem then
is to stop the contacts arcing. Some of these relays have in-built
suppression resistors, but AIUI an RC snubber is better

Also I remember a thread where someone was switching the load
initially with a semi (could have been an SCR) to avoid the arc,
then turning the relay on and SCR off. At disconnect, same thing

The semi is on at the time when the contacts open/close. If this
is an acceptable use of a semi, I'm sure you could somehow
maintain isolation between drive and load

This pdf helped me with a couple of other problems, maybe you'll
find something useful, perhaps wrt to contact material (automotives
generally use silver it seems)

http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3236.pdf

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