I want to add some more tie downs in the bed of the truck. What hardware should I use to attach them so there wont be a corrosion issue. Stainless?

 

whatever you use I would put some sort of barrier in between. try a rubber washer or something like that.

 

Important: Fasteners or coatings that should be avoided

The items listed below can accelerate galvanic corr
osion in aluminum and should be avoided. If a steel
fastener must be used it is necessary to properly isolate from contact with the aluminum.

self-tapping screws
steel rivnut
steel pop rivets
steel spring clips
RTV silicone
stainless steel fastener

https://www.fleet.ford.com/truckbbas/non-html/Q-222.pdf

See the link for prefered fasteners and methods.

 

You can use aluminum. Powdercoated aluminum would be perfect.

 

In the aerospace world we choose what will corrode and make that the easiest place since corrosion is like water in that it will take the path of least resistance. To do that I would recommend:

1. Drill your holes.
2. Apply a self etching primer to the drilled area.
3. Apply a top coat to the drilled area.
4. Use a good cad plated steel fastener.
5. Install a bare aluminum washer between the aluminum truck body and the steel fastener.
6. Apply a moisture proof top coat above all of this.
7. Optional if in a watery area, apply a sealant in the drilled hole to isolate the steel from the aluminum.

The main goal is to limit the surface area in contact with the dissimilar metals. Most of these should have been done with all steel vehicles but were often overlooked.