Best TAPE for sealing leaks

[B and C]

I've tried both scissor's and a box cutter. The box cutter wins hands down.

 

[Gypsy108]

I will get a box cutter .  I do have mineral spirits for cleaning …

Thank you !!!

 

[Calaverasgrande]

Stay away from silicon caulk.  It is a bear to remove if needed.
Butyl tape left to the elements will dry out, crack and leak unless protected by a flange or...  I tried butyl tape on my back window and it lasted about a year before leaks started again.  The butyl tape sealing my fantastic vent has been in place for over 20 years and still doesn't leak.
I also tried the aluminized flashing tape meant to go around doorways in houses.  It did not hold up to being exposed to the elements either.
Eternabond tape has been made to withstand the weather.  Use what is proven to work, not maybe's.

Haven't had a problem with silicone caulk myself.
Sure it's a mess to remove, but that is the point. It seals the gaps and stays put.
I learned my lesson the hard way on my old Econoline. I did the cheap easy fixes over and over. Then I got sick of leaks ruining stuff in my van. So I took it apart, silicone caulked both sides, and reassembled.
There is also that marine sealant thats black. My friend who is a boatwright put some of that on the outside of the sunroof seam a few months after. It looked kind of lame. A really excessive wide bead. And is surely even more of a bear to remove than silicone. But that stuff is meant for open ocean, so I'm sure it's robust.

 

[B and C]

There is always dicor lap sealant. Been used in the RV industry for decades. Not too tuff to remove.