I sort of hate relays. For 12VDC and a light load, I might consider a depletion-mode MOSFET and a diode to protect the battery. Much faster switching time than a relay, and quite probably lower internal resistance! Also no moving parts and much lower current consumption. There are some cases where it’s not appropriate though.

Anyway, I looked through the datasheet and you’re right – no mention of wear and tear from just leaving the solenoid energized, only from switching. Failure time also seems to increase when switching high currents. Since you don’t seem to be doing either of those things, I think you should be in the clear.