I don't know Davin. I have a 1989 17-foor Bigfoot
as well and the molding on mine is the exact same ivory (off white) color that the fiberglass shell is. Yours looks more like straight white, although it could be a lighting
issue in the photo. Mine too has some silicone glopped on the area on each side of the door, but nowhere else on the belly band. I think the PO did this on yours.
I agree with Donna though, if done right it would keep all the grime and such out of there. Every time I wash mine tons of crap spills out from behind the BB molding. As much as I detest silicone sealer, I'll probably replace mine soon and seal it properly to keep out the filth. I found an almond color pure silicone sealant at one of the big box stores that is a good match for the color of these older trailers.