I have some questions about accessing mining areas where crossing stream or creeks is necessary. Hopefully this is the right place to ask. Streams expected to be to the floorboards or maybe a little deeper
1) Is a diesel better than a gas truck?
2) How much does towing a trailer with gear or wheelers affect the stream crossing?
3) Will the trailer drag the towing rig down steam?
The main thing with any vehicle is not to get water in the air intake to the engine... some build snorkle kits to elevate the intake. And try to keep electrical dry, distributer etc. Diesels may have a slight advantage there, maybe a little more water proof. Also extend the breather tubes from differentials, tranny, transfer case to keep water out. Up to the floor boards can be pretty deep. A lifted truck/ larger tires helps.
As far as a trailer it would depend on the depth and flow of the river and weight of trailer as to whether it would be a factor. Careful about crossing salmon streams. Sounds like you have some adventures planned..