Powdercoat your pieces first. When you are ready to proceed with the painting portion of the build, spray whatever areas you are concerned about overspray with Dry Overspray Masking Liquid. Its made by 3M.
We use it all the time. Load it in a convensional spray gun and lay it on like paint. When you are done, powerwash it off...... it suds up like soap and runs off.
