YES
yes there are direct vent gas water heater available Absolutely NOT
B-vent pipe.
Yes heater vents can be painted the same colour as your walls.
You can try the Vent-Free Infrared Gas Heater taht is made for patios.
a direct vent water heater is more fuel efficient (cost's less to operate). aside from that there isn't much difference, aside from not needing a double wall flue through the roof on a standard gas water heater.
I'm not sure what you're asking. If you're asking if you can put a gas heater where an electric heater is, the answer is yes, assuming gas and vent availability.
The difference between a mobile gas water heater and a standard gas water heater is that a MH unit will use an outside air intake for combustion. That is the most important difference.
No. Gas water heaters are not all designed to use direct venting.
heater vent will not readjust to any position
Check the code for your area. Most I have seen go through the ceiling.
You can avoid that problem all together with a gas heater like Desa International GWN30TA Vent-Free Gas Space Heater