There's been a lot of discussion concerning the method to apply Eternabond to a Winnebago roof, so I tried to take some pictures the last time I did a roof. As previously mentioned, Eternabond tape is a great product, and I also found the best place to buy it online is Roofers Tools Online
They have the best price, but be sure to order it about 2 weeks before you plan to need the material. It seems it takes them about a week to ship the material, then the actual transit time.
The tape is a white material with a thick soft grey adhesive on the back of it. The adhesive layer is covered with a clear peel off backing strip. Once the backing is removed, the adhesive will stick to anything it is touched to.
In order to cut the tape, it is suggested to freeze the tape for several hours or overnight. If you are going to cut it with scissors or snips, freezing them as well is suggested to keep the adhesive from sticking as bad. Following those instructions, I found cutting the tape difficult, as each snip of the shears found them coated with sticky adhesive.
I ended up cutting a couple pieces of scrap melamine material I had (although any wood would do) and making a table and guide. Very similar to using a table saw and fence arrangement to cut the tape.
In this picture, you can see the tape being fed from the roll into the left side of the guide. A guide block is nailed to the cutting surface and a razor blade is inserted into a slot exactly 2 inches from the guide block. By holding the tape straight against the guide, and feeding it through the blade, you quickly cut the tape into two 2 inch wide strips. When I cut the tape, I employed 2 helpers (my kids) to roll the two narrow strips up as I fed the wide tape through the cutter. Only took a few minutes to cut the whole length of tape I needed.
Once the tape is cut, I would also suggest using two persons to apply the tape. When I've done motorhomes, I found it most convenient to set up a scaffold so I can walk at a comfortable height the whole length of the motorhome. Although it takes several minutes to set up, the scaffold enables the tape to be applied in one smooth application without any pausing to move and re-climb ladders. Applied in any manner, two persons really helps as it allows the tape to be held straight by one person while the other actually applies it.
The reason to Eternabond the roof is to insure the integrity of the seal between the fiberglass roof material and the gutter flange which the fiberglass is inserted behind. By keeping the material sealed and adhered to the gutter, you prevent any chance of the fiberglass from pulling out or the seal cracking and developing a water leak.
Unfortunately, I didn't take any pictures with the tape partially applied as my hands were full of a really sticky tape roll, but this last photo shows the tape inserted into the gutter. Again, the tape is applied to the fiberglass roofing sheet, and the internal edge of the gutter. I've found it easiest to insert the tape into the gutter first pressing it down into the bottom corner of the gutter as it is applied. I apply the tape the whole length of the gutter, then go back and fold it up so it contacts the roof. When applied in this way, you keep the tape bonded down as deeply as possible into the gutter where there is a smaller contact area. As the tape is folded up over the existing caulking and contacts the roof, it will not cause itself to be shorted on the length in the gutter.
Important item to remember, the tape should go all the way down into the bottom of the gutter, and be pressed in well there. Then lay it up over the gutter onto the roof. After Eternabonding the gutter to roof joint, as an optional item, applying a 4 inch wide strip of tape covering the joint of the front cap to roof is a good idea. In this photo, the front cap is not yet taped, but was done so after the photo was taken. The front cap tape comes down on each side and coving the end of the tape we already applied and ends right at the lower edge of the previously applied tape.
I should mention that the tape in the photgraph has what looks like vertical lines in it. These lines are from wrinkles in the tape when it is spooled in tight rools by the manufacturer. You can actually see one of them on the tape in the first picture when it is being cut. Those lines are not wrinkles in the applied tape, and will fade once the tape is applied. You do not want to get actual wrinkles in the tape adhesive when you apply it. While it shouldn't cause a leak, the appearance may not meet your expectations if you get actual wrinkles in it.
After applying the tape, unless specifically looking for it, the tape is not noticable. It blends in well with the white gutter and white roof.