Hi. I don't have experience giving birth in a hard tub, but I had imagined giving birth in, say, my bath tub (back when we lived in a house with a big "garden" sized tub) and compared in my mind to my preference (a birth pool). Maybe because I'd already birthed in a birth pool or ??? but I felt right away each time after like I really liked the blow-up pool... and not just any pool. I know some have done well using the "fishy" (kids) pool but I found myself the last two births wanting be on and push on my knees and needing extra support (the air chamber in the La Bassine and some other blow up birth pools are vertical for extra support) but also extra cushioning because my knees cause me pain sometimes. I've used the La Bassine pool 3 times now and the last time I put two sleeping bags under it and it was even better. I like that the edge was something I could sort of hug on or lay on, rest on, hug. That is something you won't get with a trough or thin edge, unless you were to take one of those foam pool noodles (a good thick one) and slit it and put it up on the trough. If you did choose a trough or tank I would just be mindful of how cushioned you want it and how to accomplish that and if you wanted the option of leaning over the edge comfortably how you'd accomplish that (towels, pool noodle?). I don't know how much those would cost but I think I purchased La Bassine for close to $100 - looks like they are $120 now. I do like your idea of being able to re-use the trough or stock tank, though :) I just opted for the birth pool because I had a feeling I'd be using it again for another little one and I also know quite a few friends that home-birth so I figured I could always pass it to another mama or something. Before I had my own I had borrowed a friend's twice and we even patched a few small holes in it (it had been "well loved").
Setting up is probably going to be easier in a trough/tank, as long as you're not having to drag a very heavy one in. We tried blowing up the pool before-hand but my littles couldn't resist getting in it. There is a neat one with a lid but it was more expensive and I imagined my kids might pull the lid off (but it would probably keep the water warm 'til you get in during labor/birth). My husband was able to get the pool set up pretty quickly but since my labors are now getting shorter it was a shame to have him focused on setting up instead of being in a physically closer way of support to me.
I think you will do well with whatever you find and feel a peace and comfort about using and I think you can make it work for you. I'm just throwing out some comparisons and pros/cons and some ideas. Hope it was helpful.