The Gen 1 alternator puts out I think 50 amps? Its poopy low though compared to modern alts that put out the 150 amp range (im pretty sure)
Daisy chained 2-3 batteries secured down in the back of the truck and wired up to solar panels on either side of it.
Throw in a hard switch to bridge the power and it could suffice to start the truck in a bad spot or power auxiliary stuff like a TV or a raspberry pi mini computer.

Mini computer like a raspberry pi might also be helpful and efficient for use as an mpfi, efi. Id really like to have one for this purpose as its way way less expensive and more powerful then oem ecu's or that instrument gauge box. It would even be possible to have a setup using a mini computer to just watch the engine operations and have is own freak out signal when it has a measurement like oil pressure drop lower then a set value or higher. The possibilities could really be endless with a mini computer on board