Do you have metal mesh inset in the lid to support the light fixture? If not, the fixture will probably get hot enough to melt the plastic, and you don't want that for several reasons. If you do, then 30 watts might very well not overheat the area, but I would want to test it without the snake in there first to be on the safe side. Alternatively, you could try reducing the thickness of your substrate or upping the temp on your heat pad if those are options.