you will surely have to clean them more often the more you add to a tub.
with as many as you have per tub i surely wouldnt let a mother have a litter in there you will have problems.

as for the "high white" i havent ever got megacolon in anything! let alone what they say is "higher risk", but that doesnt mean it cant happen in other variations. either way megacolon would more depend on who he got the rats from and if they have ever had megacolon in that line.