the OW RTW rules are very complicated and also very confusing - not only to the passenger but also to TA's and the airlines themselves. in my experience every person i have approached with a question has given me a different response.
In India for example BA in DEL and BA in BOM differ in their interpretation of the 5 Asia sectors / stopover rules. One says no problem and the other doesnt allow it.
The best option is to take your itin to the airline or TA and ask them to issue it. if nobody objects take it and run .... if they object propose something else until you get what you need.
i'm strongly in favor of OW issuing some type of uniform rules manual or something so people dont waste so much time with their RTW fares.
BTW - the OW RTW is not as good / flexible / competitive as the *A RTW however the 3 CON fares are sub stantially cheaper. so if you have a simple itin OW may be better but for complex routings *A is much better - my opinion
oh yeah - the BA/QF lounge at BKK does have showers. when you go down the escalator turn left and go into the passage way and the showers are back there.
good luck