Paul, I think that big white box in post #3 is a battery box, it looks to have vent on it.
SnowMountain,
I didn't think my '04 Hawk had an Iota converter in it either, but digging around in the cabinets I found it, also discovering a blown output fuse. That said, with a 15 amp service (that outside connection) I doubt you have one. Follow those big wires from the battery, see if they are connected anywhere else beside the fuse panel. Another thing to look for is an AC breaker panel, there will usually be a separate breaker for an Iota.
On the DC truck connection, you can certainly use the big wire you have, make sure to fuse it properly on the truck end - typically a 30 amp automatic breaker. Somewhere in the circuit you'll also need a battery separator or automatic charge relay to ensure you have a charged battery to start your truck. This can be mounted under the hood, or in the camper.
I would recommend a large fuse added near the battery, preferably within a few inches of the + terminal.
With 6 DC fuses pictured it looks to have the normal loads - Lights (In/Out), Smoke/LPG detector, Heater, Cig lighter, Battery & Water level monitor. It does appear from the external vents that you have a 3-way refrigerator though?