I am having trouble getting two surfaces to blend smoothly. The render reveals how this connection is abrupt and does not transition well. I have corrected the tangencies of the curve ends but the area in-between are still not as smooth as I would like (see rendering).
it looks like the end of your ‘shell’ is the problem, if you zoom in it doesn’t look great, the problem might be the curves you created this main shell section with, and also for the end cap/dome you could also use the loft command
Here is two ways of handling this. One hard using a trimmed back helper surface. One easy just capping the ends and filleting the edge. I would also recommend simplifying and smoothing the main surfaces first.