I’ll chime in here.
My bed is quite solid for a truck that saw salt covered roads, but my truck did have a drop in liner for I don’t know how many years, but it was in there long enough to remove the paint in some areas to bare metal. While I did have my bedsides off for prepping, the same technique can be applied to any assembled bed.
1st thing to do is empty the bed and hit the bed insides ALL over with high pressure compressed air at a close distance. You will be surprised at how much junk and factory paint will flake off.
2nd thing to do is to wash the inside of the bed with some form of degreaser like spray 9, purple power, etc. and use a good brush to get into nooks and crannies then wash it out with a power washer.
3rd use a coarse wire wheel cup on an angle grinder. The this will help break up and rough surface rust and smooth raised gouges along with removing more loose paint.
4th 80 grit on a DA, keep going until you think it’s good then spend another 2hrs going over the bed again.
5th blow out bed again with air. The last thing you want to do it sand something into the bed that you missed during pre-coating and paint over it.
6th take new 80 grit by hand and sand all the ridges inside and out…….again.
7th 120-180 grit on the DA and repeat steps 4 thru 6
8th by this time the bed should look pretty “rough” which is good it’s at this point that I will wash the bed again with degreaser and blow dry the bed and look for shiny areas of paint that I may have missed. If all is good then I get out the red scotch brite pads and go to town
9th an optional step depending on preference ( I always do this step bc all the supplies are already out ) but I will wet the bed and spray some degreaser in there and use a new red scotch brite pad while everything is wet and then follow that by steel wool pads with the soap in them already to really make it clean. Name of the game is clean prep and you will get clean results.
10th wash bed out and then degrease one last time. After the bed is blown dry out of all the nooks and crannies with the bed down with acetone or lacquer thinner on a clean throw away blue shop towel. Keep wiping and flipping until all grease comes up. Also wipe in one direction only.
11th once bed is dry you can lightly spray any bare metal spots with self-etching primer and let it dry fully. Only a little bit of that stuff is needed on the bare metal.
12th mask up the areas that you don’t want any overspray and blow out the bed and lightly wipe one last time.
13th spray time. Spray whatever your choice is and follow the instructions and directions on flash time and coats etc.
14th peel off the masked off areas and sit back and admire your work and then posts pics here on the site
Phew. That was a lot, I think that’s the most I have contributed in a single post.
Here is what my bed looked like before/after
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