We have horizontal tanks
- You fill it in the upright position.
- The outlet is offset so when you lie it on it's side, the outlet is on the high side.
- There are feet on the bottom so you don't accidentally fit it upside down.
No you couldn't reasonably retrofit a normal tank.
That said, unless you really need a horizontal tank, I would suggest avoiding it in the USA. Get a standard BBQ tank as places to fill tanks are a pain to find and usually require a car to get to. BBQ tank trade
in places are all over the place.