thought I would give a quick update, in the event someone else may be doing this same repair in the future.
Initially, as noted above, I visited an RV place and bought a set of window frames (apparently a standard size used by a lot of manufacturers) which had no accompanying sealant/gasket. And as further explained, things went a bit south and I wasted a roll of butyl tape. Also spread silicone on the inner track, which prevented me from returning the frames (see later).
Took a chance and visited a second RV parts place (farther distance from home). Funny enough, found the same set of frames WITH the sealant material (small bead of foam-like sticky stuff) already attached, exactly the same product which had been on the old set I removed. Unfortunately, because I laid a bead of silicone to the first set, I could not return them and purchase this set.
So, the moral of the story, there are window replacement frames available out there with sealant already affixed, which makes the whole job way easier.
Not sure why the first place did not have them, nor did they know about their existence. I even took the old frame in, with some of the old sealant still on, and showed the guy who "helped" me.