The last Dogboat I saw was in 1968 or 69 on the River Dart. She was in very poor condition, and had been in use by one of the Sea Scout branches if memory serves.From what I have read about the Dogboats, I think that they were all pretty tired by the end of the War,as due to their design they tended to be driven harder in heavy seas than was ideal.In the book Gunboat 658 by Leonard C. Reynolds, he records how the boat had to be reinforced amidships by steel girders when she was in service in the Mediterranean as she was strained due to the pounding taken from driving on in rough weather. From accounts of the boats they were good sea boats at speed, I imagine like the B Fairmiles. Also the Dogboats appeared to suffer more with problems of dry and wet rot. This was undoubtedly due to poor ventilation, and inherent in their design and construction. I heard stories from people who worked in the yards where some were built, that after the early years of the war, all the best seasoned timber had been used up, and boats were sent to sea with whatever quality of wood was available, bearing in mind that they were only intended to last 5 years or so anyway. The B's were easier and more economical to convert, being twin screw, (whereas the Dogboats were quadruple screw,) and having an easily driven sea kindly hull. HDML's were also used, and because they were equipped with British manufactured diesel engines, some like the Pride of the Dart kept them installed for many years. She had Thornycroft RL6's and the original bridge telegraphs. They were eventually replaced with Perkins 6354's and bridge control in 1971. The Devon Princess, however, had twin Leyland engines that had been marinised after military service!
I never heard of any Dogboats being used as a passenger carrier, although there was a novel published some years ago about a Dogboat that had been converted for use by smugglers and gun runners. There seemed to be a ring of truth in the story.
Regarding the Norwegian proposals, their Navy did crew a few Dogboats, and B Fairmiles based in Lerwick, so maybe there was some link with their veterans at that time.