Toyota has a smart alternator and will need and "booster" to charge a second battery. I have a 200 Series Land Cruiser and got a booster from Australia.
It replaces the alternator fuse and makes the alternator think the battery needs more voltage. Works great.
The Alternator Voltage Booster was the first of its type on the market and is the only unit available that was has been purpose built for alternator voltage boosting.
www.hkbelect.com
The 12 volt line on the 7pin is not enough to charge a battery. A good easy way to charge your trailer battery is a "Toad" charger. Just run cables from the main battery to the rear of the truck and connect to the trailer battery using a small charge controller . I've used this system in three trailer with great success.
Automatic Battery Charger/Maintainer for Motorhomes
www.lslproducts.net