I'm not sure I understand the first part. Are you asking if it can be painted?
For the second part, acrylic can withstand moiture very well if you use the right kind. Cell cast acrylic is much better than extruded. Cast will absorb about 4% whereas extruded is more around 10-12%. The higher absorbtion rate of extruded is what causes it to warp somewhat (that could also be attributed to poor contruction or using the wrong thickness for the job). Cell cast acrylic is used to make aquariums, so it can handle wet environments just fine