Isuzu stopped selling passenger vehicles entirely in the US about a year ago, so there really is no dealer network to support you in this claim.
If you wish to formally complain about this, contact NHTSA and Public Citizen. They might be able to help if this is not an isolated incident..
http://www.nhtsa.dot.gov/
http://www.citizen.org/
It would be difficult to prove there was a design flaw inherent with the vehicle, since the fire took place so long after manufacture. Realistically, the vehicle is 10 years old. There could well be wear, maintenance and damage issues that could have contributed to this problem, such as damaged or frayed wiring harnesses, the presence of leaking or accumulated oils, grease or fuel from worn, old or leaking gaskets. Repair and maintenance of these components is your responsbility, not Isuzu.
For these reasons you would have better luck holding the manufacturer responsible for an interior electrical fire, instead of one around the engine. (Ford had a problem with this about 10 years ago with some models and issued a recall, I believe)
As for insurance...... imo its always a good idea to have a close look at your policy and see what's covered. Sometimes, agents or brokers are so focused in selling the lowest rates they neglect to advise clients of the best coverage. In my experience, fire coverage is a seperate item, which is not always included in a policy. One should not assume its included. In my policies, fire coverage is actually very inexpensive, just a few dollars per year.