Brendan
I might be able to help you with a homebrew 2M coax collinear. It is already made and in electrical conduit with a SO239 on the bottom. It originally had 3 or 4 x 500mm aluminium tube ground plane radials but not sure where they went - easily enough replaced though. Not easy to transport as it is about 5-6 metres in length (will need to measure it for an exact dimension, later this morning ???).
Being conduit, it doesn't have great vertical stability but hanging it from the top by a rope over a branch then a vertical stabilising rope at the bottom via a spring to a tent peg (or other) into the ground would work.
I don't recall where it resonated in the 2M band, probably around 147MHz.
Needs a coat of paint to match the tree trunk to make it disappear
Doug
Revised 10AM : 5.4M long, looking a bit tired but
probably works. My recollection is that it was a virtual copy of the 6dBD Scalar G22 VHF base antenna but made with electrical conduit (part 32mm/ part 25mm/ part 20mm / part 16mm) in lieu of a fibreglass housing. Needs 4off 10mm dia aluminium radials each about 500mm long.