Thanks everyone for the replies.
2oldman - thanks for the links.
Bumpyroad - The guy in the video recommended Sikaflex 1a or Sikaflex Self Leveling Sealant. I checked the Sika site and they have a section for "Caravans and Motorhomes" in which they suggest Sikaflex 221. (although their descriptions for 1a and 221 seem similar)
Valhall360 - Perhaps cost has something to do with the manufacturers not switching over long ago. One would think they would use stainless steel screws too, rather than the ones they do use, which rust (10% of the screws in my previous trailer rusted and fell out. I replaced all screws with stainless steel). I would certainly not ignore routine inspections/maintenance regardless of which product I use. And Sika has a product to take off their sealants should any future owner require.
Funny thing, this morning I dropped into the local RV supply store to pick up some Dicor and other stuff and found a shelf full of Sikaflex products. Because I was in a hurry and all staff were busy, I did not have an opportunity to ask about these products so picked up the Dicor and left. Will have to drop back and ask specific Sikaflex questions in a day or two.
Thanks again,
Marv