You can safely lay them down and transport. With acetylene just let it set upright for a day before you use it.
Been doing that for 55 years with no mishap.

Teflon tape is for pipe fittings. Anything else will cause problems.

If you are just trying to prevent leaks, why not flow solder into the weld area?

Is that called "walking the knob?"

You need a little tiny Tig Finger to go over that.

Contaminated bottle of gas? Twice had problems with water contamination, acted like gas off or leaky system.

Check this out, shows how maleable a gas weld is for thin sheet that needs to be worked after weld. Half way through the vid. he really beats up weld area then straightens back out. This is probably one of the very few times the torch wins over tig.---RG Otto, I'm so old I forgot what my habits were...

Oxy/fuel produces a more maleable weld that will planish smooth without cracking. The weld bead is usually flatter and less bulky so there is less filing.

3003 h14 oxy/acet weld with 1100 or shear strips of 3003 for filler.---RG

How thick and what kind of weld?

I had the same problem. The welding gas supplier tested the tank and found water contamination.

This may help. http://www.esabna.com/EUWeb/FM_handbook/577fm10_3.htm