I have only used the roof seal but the web seal uses the same adhesive and it is powerful stuff, do not allow it to touch anything that you do not want it to stick to. The web seal may be more appropriate for your situation. I would recommend using the 4" and do the proper cleaning recommended for your type of roof be it EDPM, TPO, fiberglass or alum.. For instance you do not want to use any petroleum based cleaners on a TPO roof or anything that leaves a residue. Eternabond has the appropriate cleaners. Peel the backing as you go and use your free hand to smooth it down working from the center to the edges so as not to trap air bubbles. The rest of the roof may just need a cleaning and maybe a conditioner if rubber. Do a search on this site and others for more info., knowledge is the best way to attack the task correctly and avoid making a bigger problem.
"Got a dog for my kid, the best trade I ever made"
Bob, Rita and the better half of my trade, Pudgy
2011 Serrano, 2012 Jeep Patriot on tow dolly