Your going to have to set up a divider or tray that will allow the water to pass though the mechanical filter media. You could do Sock filtration in the first part of the sump and then do some filter pad media across the drip tray. This would be plenty adequate to do the job and keep your bio media clean from build up as well as make your water sparkle. Normally you want the heater in the sump where it can fit. I normally put mine in with the pump laying it down flat on the bottom. But im not sure yours will allow you to do that unless you drill the side and sue a special bulkhead fitting that seals the end of the heater into the sump.
Egon Is correct. Sorry I mistyped earlier. I meant to say you could do the sock filtration OR the fliter pad media. You could do both if you want but not needed. The filter sock would work perfectly. I run 2 of them in my sump. Both currently are 200 micron. You can get them finer or less fine. I think for the most part 200 is a good balance number to start with. Egon is also correct in making sure your sock is set up so it wont flood over if it clogs. You can make a really easy sock holder from a piece of PVC with either sections cut out or holes drilled all over it so it flows down and through. You can also Zip tie it in place. there are all sorts of methods. And yes you can put the heater anywhere as long as its submerged (assuming is a submersible).
