snap-ez makes ones in very large sizes. the AIO trainers will not hold a ton, but the stuffable ones can be as absorbent as you want them to be - i'm sure a microfiber towel would probably do the trick, or if it was a really heavy wetting situation a microfiber wrapped around another type of stuffer.
i don't have the stuffable ones, just the AIO's, but the legs and the waist are made with FOE, so they are very easy to pull up and down. we used them for EC with DS so i was pulling them up and down all day long - easy even with his fat little thighs
the 3T size (which is what my chubby 30 pound 15 month old was wearing) also fit my 35 pound (or so) then 3 year old - i tried it on her once just for giggles to see if it would fit, and it fit quite nicely.
we tried a load of trainers before we found one we liked. the SEZ were in their own league as far as quality. as soon as i found those i sold off everything else. they are expensive, but for an older child for night time you would only need a few, and they have excellent resale value.