If you don't mind kind of mottled, then that big trug thing'll do. It won't be easy to move the wool around in it, but it's do-able, especially if you have patience.
If it sits still too long and not soaked right through, then you'll get uneven dyeing. That's why at least at the start when the tea dye is fresh and still warm that it's worth the effort to get it moved often.
Best advice, wash the blanket first and put it into the dyebath while it's still sodden wet. That'll help make the dye take up a bit more even and the wool won't be such an effort to soak through. It'll also loosen and get rid of any grubbiness on the blanket, and remove fabric conditioner that won't let the dye pick up too.
Mind and not thermal shock the wool; no cold into hot or hot into cold, and the wool can sit in the dye bath for weeks without any problems. If it does ferment (guess how I know ? ) it washes out easily enough…..and this is from the woman who left a dye bath for a Summer while she worked away from home and came home to have to pick bloodworms out of the wool
beautiful rich dark red coloured wool from an exhausted madder dye bath though
and the robin and the blackbird feasted happily.
M