If you are going to Thailand, try to meet up with Nonn Panitvong of
www.siamensis.org (check out his trip reports and underwater pictures of Thai habitats! e.g.
http://siamensis.org/survey/s049e.asp,
http://siamensis.org/survey/s049e.asp,
http://siamensis.org/survey/s045.asp). Let me know and I will try to connect you both.
The only vermin you'll likely encounter are leeches, and the odd snake or two. Peat swamps are not mosquito friendly.
Even a day's stopover in Singapore will be more than enough to sample a couple of crypt localities on the island, while the habitats in Johor are 2-3 hours drive away.