Hello!
I also have been searching the past week or so for a good sealant. In talking with Heartland I got this information...they currently use Sikaflex 505UV and 521UV. Both are a silane terminated polymer (STP). Heartland told me any good quality polyurethane is OK.
HERE is a page at Sika of the sealants Sika recommends for Transportation/RV applications. The problem I am having with the Sika products is I can not find them locally. Not at Lowes, Home Depot or even our trusted Hardware Sales store.
Some others that look to be appropriate and available in gray are
Sonnolastic NP1 and
ChemLink M1
The gray tape stuff is butyl putty tape similar to
THIS It can be found quite easily.
I personally would avoid silicone sealants for most outdoor RV applications.
I will probably mailorder the Sika products or the M1.
Let me know if you find any additional information!
Best Wishes!