Dry chem. is the only way to go for compactness and overall fire protection. Most fabrics in todays vehicles are flam suppressing to a cigarette or other flammable source. Errant firecracker or roman candle ball. Any thing with old fabric seats 1960's or older my not be as flame retardant.
As far as camp fires it still tough to beat water and sand dirt on top to make sure all coals and embers are out. Those of you living in dry and heavy forrested area would be wise to make sure that plenty of sand/ dirt was put on fire site before leaving camping area. As Smokey would say, "Only you can prevent forrest fires." TJ