The "white stuff" is giving out on a lot of trailers that I have worked on, its adhesion properties to new
fiberglass can be questionable when the sealant is applied to soon
after the curing process and
the amine blush
is not washed off (with soapy water) prior to application...A fiberglass safe solvent which leaves no residue should be used in a second wipe down on mating surfaces letting it dry before the white silicone
based stuff works well.
The info I got was from a chemist I work with...he is smarter.
I know this is more than you asked for, its all about modern chemistry today and salesmen who represent huge companies and their products and costs to purchasing agents...Calling the RV manufacturers can help if they are available...But that does not always work...Parts departments will tell you what they are currently selling but not necessarily what it was built with.
I also note here that manufacturers do not exactly feel the obligation to build beyond the warranty period, some better ones feel a lifetime of an RV is 10 years...Not exactly the common owners point of view...at least not mine...This attitude is often in the decision process when materials are purchased for their RV construction as well as RV costs.
Fiberglass cures with an amine blush that can react with the adhesion properties of silicones (acid cured) if you want to use the same stuff that's ok...but what that "stuff" was
is often lost as information after a production run...more yet after a few years down the time line, the information just was not important enough to record.
It can even change year to year by the manufacturers of the adhesives themselves...
The recipe of the adhesives change as their formulas evolve according to market niche requirements.
Generally, make sure to wash the amine blush off the seal mating surfaces (shows as a powdery white) with water and mild soapy water...then dry, use a safe solvent to clean the area and re-apply any quality RV sealant.
A good test to determine composition of an exsiting sealant as a pure silicone one is a lighter test...The silicone will not burn well, the others melt and burn like wax.
GE had a recall on silicone sealants...that failure in chemistry was awful for me...I had boxes of it...It took 7 months to get the credit from them.
I still like the corded stuff...Its known at the counter as gasket cord or cord putty, region names change...describe it, they will know it...in catalogs its known as butyl tape.
One exception to this...If the sealant was the only means to hold the vent in place
...ie. no scews or fastners used...then you MUST use a sealant/adhesive
The most popular manufacturers of current good RV sealants are Silaflex 221, Parr parlastic sealants are being used now...The older silicones were popular in the 90s.
I would caution fiberglass owners on water vulnerabilities because the illusion is they are plastic and "water proof", they are not "water proof"... the gel coat when intact is... that notion of "water proof property" gets compromised in any penetration of the hull gel coat,
the glass fibers beneath it will wick moisture and cause swelling, blistering or cracking from within or rather behind the gel coat.
Like the hole penetration for your vents etc.
Have many years of RV fun, those are really great trailers, taken care of it and it will last longer than we will live.