I decided upon this trip just a few days before departure, and bought a relatively cheap return ticket with Aeroflot from Oslo to Bangkok via Moscow.
Trip duration: 6 to 27 July 1998.
Route: Arrival in Bangkok. Bus to Hat Yai, and then to Songkhla, where I found a hotel to stay. I met some Thai people and was invited to a villa in a nice area near a lake, and stayed a night there. Bus back to Hat Yai, and then crossing the border to Malaysia by land, and further on to Georgetown, Penang (Malaysia). Ferry to Belawan in Sumatra (Indonesia), and a bus to Medan. Bus to Bukit Lawang. Bus back to Medan. Bus to Danau Toba. Then finally bus (and one ferry) all the way back to Bangkok (via Medan, Belawan, Penang, and Hat Yai). Departure.
It was extremely cheap in Indonesia at the time, since the Rupiah had crashed to 15.000 to the dollar, compared to 2.400 to the dollar on my first visit the year before.