What kind of roof do you have? rubber, fiberglass, aluminum?
The 3M is great tape. Just get the 3M, none of the tape is expensive.
Don't use Amazon. Ebay has it too and is not funding the hatred of America. Do your homework on where your money goes.
Tape works great for a quickie fix. Long-term is another story. Eventually you will need to re-do, remove or re-work your fix-it job. The tape makes a mess. If you can do your job with Dicore Lap sealant then use the sealant, NOT THE TAPE!!!
The tape will leak anywhere there is a small angle or crevice as the tape cannot fill in little gaps, you will have to supplement with lap sealant anyway to fill the gaps the tape leave behind, or water will get in and rot out what you think you are protecting.
Don't use the tape to waterproof the camper. Do use tape to tape down solar panels so you dont have to drill holes, or to make a patch over a hole on a flat surface. The tape has its place, but not for your purpose.