Dip at end of hallway.
New member here. I am prepping to install CoreLux Rigid Vinyl Plank in my house. The planks are 8.9” wide. I am planning to lay it perpendicular to the hallway in the attached photo. The photo show the wall at the end of the hallway, with doors to bedrooms on each side. While checking the hallway floor for flatness, I found that there is dip starting about 18” or so from the wall in the pic, which reaches a depth of 1.2” at the wall. The same dip wraps around the bedroom doorways on either side of the wall as depicted in the photo. I am planning to use transition moldings in the doorways to make the install simpler to do in stages as I am working alone. What would you recommend to fix the dip? Henry’s or roofing felt? Also, if I use a product like Henry’s, do I need to cut the bottom of the casings and jamb before applying it? Thank you.