How long will a deep cycle battery run a set of warmers?
Most deep-cycles seem to be in the neighbourhood of 85 to 100 Amp-hours, actual capacity varies with discharge rate and temperature and a bunch of other things, but basically, it will be in the neighbourhood of 1.5 hours or less of actual heater on time per battery. I don't know how often the heaters are on once the tires come up to temp so I don't know how long you would actually get.
Don't diesel trucks have 2 batteries because they run them in series for a 24V starter? That doesn't keep you from putting them in parallel for the inverter, but they won't be deep cycles and will be ****** if you flatten them. The number or size of batteries basically doesn't matter as warmers seem to be able to kill any batteries quite quickly, you need power going in at roughly the same speed it's coming out, therefore a huge alternator.