Good advise about engraving,but through experience the Thief's don,t care ,I only leave outside a 20w panel to trickle charge, my big one  will be pole mounted,so I can easily take it down ,and put inside when back in the UK.
I do find e bay best for panels etc ,but then you have the big expense of getting it  all to Spain'
I would say the Batteries are the biggest outlay, I,m waiting for the stand by batteries for the generators at work to become available, they swap them out every 3-5 years(mega expense) ,and I would have hoped that you should get close to 10 years out of a well maintained  battery,25 years life on a solar panel. ;)