My success with tuberous begonias vary considerably. I only had a few of the park Wopper germinating. I think you need to mist frequently with a very nice nossle (windex atomizer type bottle) and keep temperatures around 75F. They are very sensitive to drying out or change in temperatures.

As you have had success with Gloxinias and other begonia seed, your lack of success maybe due to the seed. If you put it onto a sheet of paper, tip the paper up and tap it, any good seed will roll down onto another sheet of paper placed to catch the seed. I have bought seed in the past with only dust in the packet, and not a single seed.

I do a lot of hybridising, and grow a few thousand seedlings each season, giving them a 14 hour day, and set the temperature at 75f. Germination takes between 8 to 14 days, although at a lower temperature it could take longer.

I posted this on the other topic ...

I got 4 Whopper Yellow sprouts today !!

I moved my seeds to a warmer heat mat, started keeping the grow lights on 24 hours and I'm making sure I keep them moist by spraying and/or bottom watering. I'm not sure it this has helped or if it was that they just needed more time to germinate.

I also have one Begonia Bayou Scarlet that sprouted yesterday.