Another option is a battery equalizer like this one, allows you to tap off the 12v center tap, and the equalizer keeps both batteries in balance preventing un even discharge. I've been using this setup for the last 5 years with no problems. Decided to go with a third battery to completely isolate the 24v system from 12v for better piece of mind. Plus there are minimal options for 24v solar to recharge batteries when camping remote without relying on alternator only.
Battery Equalizers
vanner.com