On Thursday, March 15, 2018 at 2:05:38 PM UTC-7, wrote:
On Wednesday, March 14, 2018 at 1:22:11 PM UTC-4, Jonathan St. Cloud wrote:
My trailer arrived with two soft solar chargers attached to the roof top via a sort of caulk/goop. Two years later the trailer is leaking under the solar panels. Looking for a recommendation for a goop or caulk that is white or clear, and can withstand the sun and heat of the Western USA flying spots?

Sikaflex is usually the "gold standard" in the RV industry. Any exterior penetration gets sealed with Sikaflex. Excellent caulk.

Both the Sikaflex 2xx and 3M x200 series are polyurethanes and they have similar and equivalent product lines. Both big in the marine and RV business. The 3M is perhaps a little more available in the US, but both are widely distributed. In 3M, 5200 is the strongest bond, 4200 is weaker (easier to remove later). Both come in a slow cure (like 72 hours) and a quick cure version (24 hours). 3M also has 4000 UV which is not a polyurethane, but rather a polyether. The bond is something like 4200 but it is more UV resistant. All of these products are very messy to work with, I recommend tightly masking the area around the part or fitting, immediately removing all of the excess making sure you have plenty of paper towels and a receptacle to put them in (or you and your trailer will be wearing a lot of it). Then immediately peel the masking and leave it alone until cured. A thick bond line will allow more differential movement between the pieces before failure, the most common cause of sealant failure. They are aggressive moisture curing adhesives, meaning that once the seal is broken they will eventually harden in the tube, so don't buy a lot more than you can use.

On a well prepared surface, the bond strength of 5200 or the equivalent Sika will be sufficient to hold anything in place once it has cured without fasteners (around 700 psi claimed). This is legend in the boating industry - 10,000 lead keels sealed with 5200 will not come off even hanging with the bolts removed. There are now some chemical de-bonding agents available, but they work slowly and tediously.

Experience from extensive use of all of these on boats over many decades.