I used a hand-held 1" x 3" stainless steel stripping brush fastened to the end of paint roller extension pole using real duct tape (not that crappy plastic stuff...) to scrub with the naval jelly. Then used a 4" interior trim paint roller on the other end of the paint roller extension pole to apply the paint. The 4" wide roller just happens to be 3 7/8" wide so a perfect fit inside the bumper.
TT: 2015 Jay Flight SLX 195RB Baja Edition
TV: 2014 RAM 1500 Bighorn CC, 5.7L Hemi, 8-spd, 3.21LSD, Factory Air Ride/Tow Pkg, Andersen WD/SC