Nova

Yep considered that idea jim but for one I would be worried about taking the cover off for normal observing and having the filter exposed (I keep mine in a box). Also if its fixed on the inside id imagine its harder to keep an eye on its fixing which would concearn me as I check the filters fixing on a regular basis (but I am [removed word] like that). And I like making things lol

No reason why you can't make a scaled up version of mine. You may want to think about addition fixing methods.

thanks for the comments. so far I have been limited to imaging the moon but jupiter is now very nearly over head at a reasonable time so im really looking forward to having a go. im soon to add an auto focuser and a tal 3x barlow to my set up.