Does anyone know where I can buy a family sized tent in Bangkok (with 2+ compartments inside)?
Have you tried the sports store in one of the Central department stores...think they're called Super Sports. I've seen tents there for sure, but I'm not sure about the quality. For a good quality tent you may need to find a specialised shop...and I don't know of one, sorry!
There used to be a specialist camping shop called Shinetawan camping in the Ploenchit Center on Sukhumvit road next to Soi 2. I still have the telephone number. 02 656-8549
They also have a second branch in the Amarin Plaza according to the receipt I have! 02 684-5902