Is keeping them clean a lost cause?

My bottle babies are 4-5 weeks old, eating great and starting to taste canned food (but still prefer the bottle at this point), and using the litter box just fine. I set up an old toy box for them to be in with a litter box (old cake pan with non clumping litter) at one end and a box with a blanket at the other end for them to sleep. I've lined the bottom with plastic garbage bags and towels over top of that. They are just always COVERED in poop and litter. I would seriously have to bathe them once an hour as often as they get dirty. They track the litter everywhere and also like to lay in the litter box. Because it's non clumping the litter is always wet from their urine and when they lay in it, it sticks to them. They are *supposedly* Maine Coon mixes and are getting pretty fuzzy. Wiping them down with a wet rag or baby wipes just doesn't work. It takes a full scrubbing to come anywhere close to clean. I spent 20 minutes on each during their last bath just scraping the poop and litter off with my fingernails... ewwy.
So is it impossible to keep them completely clean until they're older? And how often is it safe to bathe them?

At 4 to 5 weeks old, are they getting any time out of the box you've made for them? At this point, they really do need to be able to run around and exercise those little developing muscles. They will also be less likely to roll around in the litter if they aren't confined so closely to it.

They do have time out of the box (a few hours a day), but I guess it needs to be more. Thanks!

with our litters we normally set them up in a room with a litter pan, food and water and enough room to roam without getting into trouble(i use my bedroom) but they also have mum to help keep them clean.
i remember when i had 2 kittens without a mum we got them at 3 weeks old but i didnt have to much of a problem with keeping them clean i bathed them fully once a week untill they was 6 weeks old if they got dirty before that i would use a damp cloth. but they also had a lot of room away from the litter tray (again in my bedroom). and they loved to play on the small cat tree i keep just for the kittens.

without a mom unfortunately they do get sooo dirty. My little fosters that age always LOVED bath time, and it is summer so you can give them warm baths. They would just go limp and relaxed. Then I dried them off with towels. Of course like you said minutes later they would be dirty again! They are just so young, and tend to get a bit confused about the litter box at first.
One time I had a big litter of orphans and another volunteer offered to take a couple, they were about the same age as yours. I bathed them and got them all clean and fluffy, and we drove them to her house. On the way over before we even got there a noticed a poop covered paw reaching out of the carrier, exploring the back seat.... by the time Jane got them they were once again filthy....it was like 10 minutes.

It helps if they can have a larger space. They'll still lay in the LB because that seems to be what kittens do best is get dirty. But if they're in a larger space, IMO, the helps because they can get away from the messes more.