A lot to your question. I am about to go through my entire toaster. Basically look at what you are sealing and what properties you need for each type of area. I used several as I was re building my trailer.
Acryl-R used for seams on the body, flow swell, stiffer than then next couple of examples.
Sikaflex 221 used for seams like the awning rail or as a first layer for installing vents. Good all purpose stuff.
Vulchem or Tempro 635 used for almost anything...stiffest flow, never cures out Great all purpose stuff....windows, vents, anywhere you need a tough covering
Parabond...some what stiff but takes abuse and heat well, aluminum colored available (I will always thank John HD for introducing me to this stuff.)
Sikaflex and Vulchem are butyl based sealants, they are sticky, do not truly cure (stay soft-sort of--), a bit unforgiving to work with--in other words pain to clean up mistakes, but the quality of those materials may cover the applicators mistakes.
I have also used a 3M flowing sealant that was quite good. Do not use silicone sealants on metal, they have citric acid involved in the air curing process---you can smell it when it is applied.
Read some of the threads on leaks or restorations. Companies like Sikaflex, Tempro and 3M make several different sealants. There are a lot of good selections. You will find suggestions other than what I have mentioned. Also note sources such as the Vintage Airstream site. The above are what I have used.
I like Vulchem a lot, sort of like Duct Tape is to Red Green
I used Vulchem to set a window it did well, I still did re-run the seam again when finished.