I've done the DOH-BKK-DOH route 3 times and I can confirm that they use Thai's lounges. OK if you go to the main lounge but last time we were 'invited' to a satellite lounge close to the gate which to be honest was poor especially with regards to the food available.

In terms of feedback on this part of the route the service has always been up to the usual superb standards I associate with Qatar's C class (except for my very first flight a few years back on the infamous old A340). They will feed you until you feel fit to burst and provide drink until your liver gives up.

In terms of hard product - if you get the 777 expect full lie flat with loads of space. On the last return there was a last minute substitution for an A332 ( I think) which whilst acceptable for a day flight and certainly a comfortable seat did lack the space of the 777.