I prefer going the vertical method for 55 gallon drums. Built a bunch of these back in shop class when I was in High School that was pretty much based on this design.
The main difference is we fabricated a round fire grate that could be moved to the higher cooking grate positions if you wanted to use it as a grill as well.
Only problem is you may find it hard to locate the round cooking grates in Bangkok, but these are also easily fabricated out of expansion metal if you have access to that.
Should look something like this when it is done, except we added a fire door at the bottom so you could add wood/charcoal if necessary during the cook.
Also, do not forget the thermometer. It is a must for getting the temp right and making great BBQ.