Will,
I have successfully used a Nikon ED50 with a monopod for around 10 years. I started with lightweight tripods around 1kg with a video head and found they weren’t much use unless I hung my rucksack off the bottom of the centre column to stabilise them. Low weight and stability do not go together ! The additional weight of the tripod (and don’t forget video heads start at about 300-400g) and the hassle carrying, folding and unfolding it wasn’t worth it. I still get a kick out of the simplicity and minimal weight of the ED50 and a monopod.
I don’t bother with a ball head or video head on the monopod. 9 times out of 10 it’s quicker and easier to angle the monopod and/or increase/reduce the monopod length to get onto the bird. I just use a Velbon quick release head screwed straight onto the monopod. However, I do agree than for high angle observation some contortions are required !
I use the monopod both standing and sitting, which is why I always carry a sit-mat in my rucksack. I have successfully done a little bit of sea watching sitting on cliff tops with the monopod at or near minimum length. I also well remember spending a happy half hour sitting on a cliff top in Cornwall watching Choughs feeding in the grass about 30 feet away using the monopod and scope.
I can hold the ED50 on a monopod steady up to about 30x magnification for short periods, but I nearly always use a partly home-made fold down foot for anything above about 20x. I fold the foot down and hold it down under the foot nearest the monopod if standing, or under my knee if seated. This completely stops any “twisting” vibration/movement of the monopod which is by far the most difficult to control by hand.
As you are carrying all your camping kit at the same time I would therefore stick with the monopod. I wouldn’t bother with the tripod feet on some monopods. I have a Velbon RUP4 which is nla, but it looks like it has been replaced by something like the UP-400. IIRC SLIK do a good range too. Last time I looked there was little weight-saving going for a carbon fibre monopod instead of an aluminium one.