Are you ready for something crazy?
Being a whitewater kayaker in my earlier days, I have accumulated a quiver of whitewater kayaks that I can't seem to let go of (contrary to the wife's requests). A few of the older kayaks have fairly significant volume capacity in them. One of my kayaker buddies told me he hauled one of his old kayaks hunting in case of a bad haul-out that consisted of a lot of steep downhill. He had twice packed boned-out elk meat by stuffing it into the kayak and kicking it down the slope for a ghost-ride.
So I gave it a shot in the mid-2000s with an elk I had shot about 2800 vertical feet off the deck of where I wanted to end up...boned the meat out and stuffed it into an old 13'/40lb Perception Mirage kayak I had brought along. Stabilized the meat in the front and back of a kayak with sticks cut-to-length and kicked it down the slope. It scooted down the slope and caught some air off a few benches and downfalls, but it probably ran 1900 vertical feet down talus and beargrass without a lick of my effort involved...and they kayak didn't suffer a crack. I figure that thing saved my knees and back, as well as several hours of effort ferrying loads. The meat was still in impeccable shape.
Just an idea. I hauled a kayak to hunting camp a couple years after, but didn't have the opportunity to utilize it. Since then, I haven't hauled again...but sometimes wish I did. I figure it looks a little strange in elk country in September with a whitewater kayak on top of your pickup

. However, maybe it's time to relearn an old tactic though...definitely a pretty useful tool if you are only faced with a wicked downhill haul. The kayak slid through thick forest and downfall with little effort.
I tried the sled method on a late day in 2009 after shooting a bull 2500' above the valley (rain came and melted the snow that was previously there). I'll never do that again...the sled was hard to handle and ended up cracking when pulling over downfall. There had better be a nice road the next time I bring a sled along for a haul...