I'll be in Phuket next month and have a long-shot question. Is there anywhere that rents waterproof housings for DSLR cameras? I can't buy one here where I live (Laos) and wouldn't want to spend that much money anyway since I won't use it much in Laos (no beach!).

Never seen DSLR's for rent here other than maybe from a private individual. Lots of smaller digital cameras available from most shops though.

All different types require a different housing. That combined with the risk of a flooding means that there really are no options to rent housings.

Some places will still have cameras for rent, often directly from the instructor who will be present on the boat. We have stopped with renting out camera's, it simply got too expensive with floodings, which especially happened with unsupervised renting out.

A very good alternative: your instructor/divemaster will probably be able to make photos or a movie of you. Probably the same price as camera rental and higher quality photos/film.