In case anyone else wonders-- going by train is very easy. On the way there, I did as Mike suggested and went by BTS to Mo Chit, then caught a taxi (89 baht). The driver knew where I was going-- Mike, the name in Thai helped as I was able to read it to him, and then later show it to him when he wanted to make sure he was going to the right place-- so that was easy.
I decided to take the train back. The station is only 1km from TOT and is a pretty straight-shot walk (and there's a win not too far from TOT, so if you don't want to walk all the way, you can take the motocy taxi from there). The train back to Hua Lamphong only costs 4 baht. If you're not in a huge hurry, this is a good way to go (if I go again, I'll take the train both ways). Here is a site that shows timetables (there is also a timetable in English right by the ticket window at Laksi); you can choose which stations you're traveling between (Bangkok to Laksi and Laksi back to Bangkok):