My plan is actually to pour some of that liquid foam into the gap and then sculpt it flush from there. I plan on stretching some plastic over the back of my cab and then masking the gap between the bed and the cab. I will then put the cap on and mask the gap on the sides between it and the cab, creating a little bucket to pour the liquid foam into. If everything goes according to plan, it will adhere to the cap and I'll just have to smooth out the top a little and it will be pretty flush with the cab. I will then remove the cap and strip the plastic away. I will grind it down a little bit and put a skim coat of body filler on it and the rest of the cap. After a bit of sanding, it should be ready for paint.
I've discovered that Rustoleum's dark gray metallic is a perfect match for the color of my truck. A few coats of that along with a few coats of clear coat should make the thing look like a Toyota accessory.
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