The main problem is storage since hydrogen is so small.

Yes that is the problem. Maybe there's some chemistry that could help with this? I don't know I'm not a chemical engineer.

I think mobile applications make more sense though, so things like trucks and forklifts.

Also airplanes. Jet engines can run on hydrogen with little to no conversion. Problem there is the low density of hydrogen means airplanes need to be redesigned to have much larger tanks, and cryogenics need to be involved. Airbus has some ideas about this, but it's still very much in the concept phase.

But for transport trucks there's an interesting solution being tested in Germany where overhead wires are run over the highways, similar to overhead wires for trains. Trucks connect to that when on the highway. So the trucks would only need battery for making stops then they're off the highway and would recharge again when back on the highway. Seems like a good solution to me, but it's still being tested.

But hydrogen could replace natural gas for heating and for those who refuse to give up their gas stoves. But as you say, it's small so the gas pipes would need to be upgraded to have tighter seals for that to work.