Thank you all for your comments. From what I can determine, either Dicor or Proflex caulking should meet my requirements. I assume there is no compelling reason to choose one over the other except for differences in price and/or availability. One wonders why the producers of these materials don't supply them in a smaller, resealable toothpaste-type tube that is more practical for spot use. I would think there would be a decent market for such a product for use by RV owners doing general maintenance. I know I would include a tube in my maintenance kit if it were available.
Charlie D., following your suggestion, I used some bleach on the caulking I have applied and it did remove some of the dingy appearance. However, I am guessing that, even though it worked temporarily, it would again attract dirt on my next trip due to the surface characteristics of the material. We shall see. Thanks anyway for your suggestion.
Regarding preserving the material in the large tubes, I wonder if some barrier to air infiltration such as petroleum jelly applied to the electrical connector cap would lengthen the useful life of the product. Perhaps the barrier could also be applied where the sliding baffle meets the inner surface of the tube after the original seal has been broken.