Well, you could carry spares just in case.

The load side of a relay is not connected
to the activation side of the relay, depending
on the failure makes a difference as to if the
relays need more Amp carrying capacity.

Poor quality relays are going to be more prone
to failure, if you are electrical enough, you could
take the bad relay and figure out why it failed.

In my case, it was a matter of dirt, didn't drown the
relay, just dust buildup, blew the dirt out and it was
fine, but this is a horn relay, not one that would see
hours of on time

A 30A relay should be able to withsatnd that kind of load without any problems. Relays don't like vibration, its worth rubber mounting it in some way. Oh and making sure its either sealed or kept dry.

Ok, I'll try to install the relays in a location that can avoid dirt or water (those are the 2 more common elements here in Venezuela) and will try to avoid vibrations by using some sort of dampening material between the relays and the inner face of the front fender.

I'm using BOSCH German made relays,  They're really good relays!!

Thanks for the advises guys!