FWIW:
The Trombetta DC solenoid with silver alloy contacts that I gave the link to above is rated at 225 amps continuous duty, and 600 amps inrush current.
But the important part for reliability with large RV battery banks being charged by high power engine alternators is the Trombetta solenoid's silver alloy contacts - that are immune to the normal corrosion of raw copper contacts.
It's this corrosion that causes the RV battery banks - gradually over time and at first unnoticed by RV'ers - to begin to not get charged as well as they should when driving. I noticed the charging voltage falloff because of my dual voltmeters right on the dash comparing engine DC voltage to coach DC voltage, but before that I was really getting frustrated arriving at campsites with the RV batteries still not charged much.
Here's more info on the DC contactor solenoid - the model is the 2nd line item on the specifications chart:
http://www.trombetta.com/images/pdfs/dccontactors/bear/bear-family.pdf