Sulphur smell is iron bacteria and hydrogen sulfide. I have a well at home and have this issue when we're gone camping for some time. It eventually flushes itself with water usage.
As suggested, you bleach the system (lots of articles will give you ratios of bleach, but you should not need more than a pint in an rv). You have to turn on your water at all faucets and make sure you have bleached water coming through them all --- hot, cold, shower, outside shower. Then, let it all sit for a good 24 hours before rinsing out.
This is all standard technique for 'shock chlorination' of water systems. No different in an RV. As mentioned, if the water going in is 'bad', of course, bleaching your system will have no effect.
Note: Use unscented bleach and be sure it is newer bleach. Bleach that has been sitting, after opened, for some time looses efficacy.
And yes, hoses can give you smells too, but not that sulphur odor.