As I mentioned above, EternaBond is used in the roofing industry for sealing all kinds of surfaces, flashing's, etc...
I stopped by a local roofing supply that I've dealt with, today, to check out their inventory...
They did have several versions of the EternaBond, but several other types and brands of sealing tapes as well...
Some of the 'others' use Butyl Rubber and Bitumen based products as the sealing media - I checked them out, and none of these types had the 'stickiness' of the EternaBond I used on our AS - As a result, I'd beware of these cheaper, more common type sealing tapes...
EternaBond says their tapes use 'microsealant technology' - and their MSDS shows the product contains a 'polyolefin & synthetic elastomer...whatever that means...All I know from personal use on our AS's roof, is that stuff is REALLY sticky, and should seal against leaks for many years...The aluminum surface of the tape will also shield against any UV damage to the sealing material for lots of years!
The roofing salesman said that they've been using these other types of sealing tapes in the industry for a long time, and that the EternaBond product is comparatively new, well suited for eliminating leaks on all kinds of roofing - which many the other sealants won't adhere too...
Sooo, if using a roofing supply to get your Eternabond, I wouldn't let them talk you into these other types of sealing tapes...
Note: I have no connection with EternaBond what-so-ever, but believe it's a great product for many of those 'leaky' situations we AS'ers may experience (SOB'ers too!)...
Here's another supplier I found that seems to have good prices...
Eternabond
It bears repeating, that if I were installing new vents today:
1. I'd use the EB double sticky tape between the vent frame and the roof surface (that stuff is so sticky that alone, it would probably hold the vent in place forever!)...
2. Then drill and secure the frame mechanically - screws or rivets...
3. Apply 4 inch wide EB (Alumbond type) over the screws to overlay the frame ridge and down onto the roof surface, all the way around the vent frame...
4. You'll NEVER have any leaks - EVER, and no ugly blotches or beads of sealant that will eventually be attacked by UV rays, causing future leaks!
Here's some more tech data I found about EB:
Composition
Eternabond RoofSeal/OneStep utilizes EternaBond’s advanced MicroSealant™ Technology, a 100% solids formulation of synthetic resins, thermoplastics and non-curing rubber (non butyl) with a built in primer, bonded to a tough UV stable backing. Designed not to harden under even the most rigorous conditions. Sag temp > 200ºF. MicroSealant™ is protected (while in a roll) by a tough, easily removed siliconized polymer release liner, which prevents contamination prior to its use. All materials are prefabricated to provide uniform thickness.
Keep dry out there...