Sorry to hear of your news.
My situation was similar after my RP, over four years ago.
My PCa seems to be resistant to all that has been thrown at it (although I've not had HT yet and that's likely to be some way off).
My PSA is at present 0.4 (highest was 0.7), I continue to feel absolutely fine.
My onco said a while back that if my PSA continues to rise, "..there are hundreds of things that we can throw at it" ( I think the 'hundreds' might have been an exaggeration but I guess that he is saying is that there are still plenty of weapons in the armoury)
My only suggestion to you would be that further to any salvage RT, push for the highest definition scan you can get even though this means going to another area - I had a Choline PET/MR scan. It's possible that with your low PSA, nothing may show up but still, I believe, worth going ahead.
Best wishes,
Dave