I thought this might be of interest to a few of you.
I've never really liked dragging deer across muddy fields at this time of year. Apart from it being hard work they look like crap by the time you get them to a dealer.
I picked up a few ex rental creates. A 135ltr is an ideal size for fallow. They're very solid and have a good lid which keeps them clean and discrete for open top pickups.
3 LARGE New Black Plastic Removal Storage Crate Container - 135 Litre | eBay
With a couple of meters of scrap box section and my old mower wheels I made a very basic trolley that the create sits in.
I have extracted deer along well used footpaths this way with nothing but the odd funny look.