As I stated in my first post
"Really wanted watercooling but also wanted it all internally"
So radbox wasn't an option.
With the fans I tried a number of variations:-
1) both fans inside pulling cold air through
2) both fans inside pushing warm air out
3) both fans outside pushing cold air through
4) both fans outside pulling warm air out
5) one fan inside one out in an offset push/pull set-up (cold air through)
6) one fan inside one out in an offset push/pull set-up (warm air out)
There were no noticable case temp differences with
any of the above setups but my GFX mosfets are around 40degrees cooler at full load with the internal fan(s) blowing onto them ie, setup 1) and 5). The final decision to stick with setup 5) was because I needed a PCI slot freeing up which the other fan in setup 1) blocked.
As for the dust filter - not been using it for the last 4-5 months and only had a tiny ammount of dust build-up in the case when I took the pics. (and as a bonus, roll the pc around and I don't need to hoover

LoL)