I think ,it is " J B WELD" . you can find it at Home Depot
It works very good .I did my old windows and reseal them with this stuff
Work great Jean-L
I'm sure J B Weld resealed your old windows -- but -- should you ever need to remove one, I think you might regret the day you decided to install them with the stuff, which is an iron filled epoxy.
You might be able to soften the epoxy with a heat gun but from my experience with the stuff I think the aluminum frame would end up extensively damaged in the process -- at least with someone of my skill level doing the job. Worse yet, I think I would also damage the fiberglass surrounding the window frame in the process.
I would advise, as was already advised, using the butyl tape sold at RV suppliers specifically for the purpose. In the event that is not convenient, a bathroom/bathtub caulk would probably be OK.
In my case I had a terrible time sealing the left-rear window which is the one that can be opened from inside in case of fire. The leaks
were not from the frame-to-fiberglass joint, but from the opening part of the frame itself. Considering the size of the window compared to my body size, the fact that it is about four feet above the ground and the thickness/strength of the fiberglass body of the trailer, I decided that in case of a fire that was so advanced that I couldn't get out the regular door, I would quite easily be agitated enough to smash a hole through the side of the trailer. So assuming the risk, I sealed it shut.
Back to the original question -- I'm not saying it is wrong to use J B Weld to seal the windows, but I would strongly advise anyone to consider future window removal.