"The 12v element draws ten amps so running it off the 7=pin should not be a problem."
The 7-pin will start out at say 15 amps but will quickly taper to more like 5 amps within say 15 minutes (you can measure that happneing with your ammeter) due to the way alternators work.
So expect a 5 amp "loss" going down the road. (Which can be made up if you have solar and the sun is out) Depends on how long you drive (10 hrs = 50 AH down) and the battery situation at the start what happens. Then you have to consider if that night you have a chance to recharge the batts.
All very situational. Could work.
BTW if the multimeter only does 10 amps as an ammeter, it should be the kind you can replace the fuse if the amps are too high. A Trimetric is safe to use for this measurement.
