We currently use a combination of fleece bedding and aspen
/CareFresh 
in boxes. This works the best for us. When we first got the guinea pigs, we used the aspen/carefresh through the whole cage, but with the cage being so big, you couldn’t just take it out and dump it, you had to shovel it out (or scoop it out). It was a pain, and used a lot of the bedding.
To do the fleece bedding, I cut up a quilted waterproof mattress pad as the bottom waterproof layer, then I put a towel down, then a piece of fleece cut to the right size.
The idea behind the fleece is that when the guinea pigs pee, (which they do every couple of seconds), the fleece will wick the moisture away to the absorbent towel layer beneath, and the waterproof pad will keep it from going farther down.
The all fleece worked well, but a combination of the two turned out to be the best.
I made coroplast
boxes to fit the spaces where they spent most of their time. One was made for the kitchen area, one under their main hidey spot, and one under the second story kitchen. Now I can fill the removable boxes with aspen and CareFresh bedding. This worked like a charm because now the majority of the mess is in the aspen/carefresh bedding, and the boxes can be taken out and dumped, then refilled. I do think that it keeps the smell down.
