I replaced my original rubber EPDM roof when I purchased mine 4 years ago. I went through 10 tubes of Ducor lap sealant. It is applied with a chalk gun. A good chalk gun will be easier to use than a cheap one. You can also purchase EPDM in cans, liquid rubber etc, applies with a roller. Use the self leveling EPDM verity on the roof. Once applied, besure to go back and check the seams; make sure no areas were missed. I check my seams every six months when I clean the roof. Lessons learned; don't buy a rig with a rubber roof if you can avoid it. If it leaks the luan underneath quickly becomes compromised. As such, I also replaced 80% of the rigs roofing luan. I used 1/4" thick sheets of marine board. Sure, I added about 150 lbs to the vehicles weight but the roof is quite sturdy now.