My two don't care where I feed them.. If I'm in a rush or just not in the mood to hang around and watch them eat, I'll just feed them in their enclosure. Sometimes I feed them outside in the sun on the warm concrete slab (they seem to get it down quicker and enjoy the warmth of the sun). I've occasionally even let them hang from my arm while eating haha, probably not overly responsible, but it's very fascinating to be able to watch up close like that, and my two never seem to mind (I don't recommend this to people, as I'm sure it could go very wrong). I just move very slowly and as little as possible, and at the end hang my arm into their enclosures and they crawl right in to sleep it off.
Daniel, if you want to feed in a feeding tub, I say go for it. All snakes are different though, and some don't appreciate being moved before/after a feed. So if you have any issues like refusal to feed or regurgitated meals, I'd give feeding in the enclosure a go. A small amount of aspen is unlikely to hurt them. If you're really concerned, you could lay down a sheet of newspaper or butchers paper at feeding time and remove it later.
All the best!