What do you guys think of using something like this? http://www.newegg.ca/Water-Liquid-Co...ategory/ID-575
If you could extend the lines and put them in the sump, it may work.
Would also have to replace the heatblock/pump for something saltwater compatible.
This might work for very small tanks, but need to watch for toxic materials that your water will come in to contact with. Salt water will oxidize metals quickly, if its all plastic this not an issue.