I'm also considering a strip to a "weather stripping" store to see if I can't solve it myself.
I would never let someone (even an experience RV dealer) rip into the truck camper bulk-head wall to replace that window. Especially on a brand new camper!
We have basically the same window (installed in our Outfitter bulkhead wall) however, it is considerably larger than yours (much wider).
We've rarely had water infiltrate in; only once did that happen, in torrential rains in Wisconsin, and while we stored it outside (for the 1st time this winter).
Indeed, I went to the building supply store, and bought temporary winter sealant *for windows* (clear caulking). I sealed up all the weep holes in that bulkhead window, and the split center. Now NO snow blowing in there at all for the past 3 months (we have a snowstorm roughly every 3~5 days here, with winds blowing at 50 to 60 MPH {the snow blows sideways for up to dozens of feet}, blasting the bulkhead window).
This clear weather seal caulking just peels right off in seconds when/if you need to. So, if this were me in your situation, I would try using this stuff to seal up the weep holes along bottom/top of the bulkhead window, and also apply it along inside around perimeter of window tracking-- where needed.
Carry a tube along on your travels.