Salmonmac,
I think you are right, after doing a test last night if I try to do this as one piece, even if I could get it all to fit on a linked-together circular needle, the dang thing would probably be so heavy I wouldn't be able to work on it

Plus my trees running sideways would look sort of flat since I wouldn't be able to do the stitches correctly to get them to look like branches.
So I think I will do it in 4 pieces 1 on each side & 1 at the foot of the bed, then I can make a nice binding all the way around the edge of the mattress.
Thank you & Suzeeq very much for responding to my question.
Cheers,
Lee