Those worried about 400amps... That has to be the peak and I doubt you would see extended loads like that (If so, you should be pausing anyway). The 200A Blue Sea I pointed out should work great. It should take 20 second peaks of 400... If it pops, no big deal just flip it back and try again. That is the beauty of a breaker vs a fuse. Seems perfect for this application IMHO. If it ever becomes a problem on the trail (a bunch of long hard pulls needed), just bypass it. Seems like a no brainer solution.
As far as acceptable risk goes, like other said, probably OK in this case. If however, you were running the cables through the interior of the truck it would not be acceptable risk. I have seen cars burn up for that very reason. The engine bay tends to be pretty fire retardant in general and with such a short run not much to worry about. I like the breaker more for the extra load protection in general (not really worried about an accident... but it works for that too).
The thing with wiring is that it is very unattended.... Just sitting in the garage some dumb mouse that likes the sweet taste of shielding can burn your truck down by causing a short or maybe some chemical spills on it, or the sun and heat just degrade the shielding, or chafing from vibration driving down the road.... it happens. Lots of insurance claims for stuff like this.
At least when you are winching or whatever (sure its dangerous), you know you are in a dangerous situation vs sleeping in your bed while your truck burns the house down. I'm not paranoid (or trying to make others), but I tend to over engineer myself. To each his own level of acceptable risk in the design. I built my deck to hold 10k lbs, overkill ~5x, but I never have to worry about it again... even if I decide to park my truck on it.