Joel,
We have boated at Lake Powell for about 30 years now and have never had any Rat or Mouse problem onboard. If you leave things on shore over night the rodents may get into them however. Put food items in Tupperware type containers if left onshore overnight. Haven't really had any problems with rodents in tents either. Can't vouch for the southern end of the lake, but no problem in the northern end.
Looking forward to seeing you again. We will arrive on PM of the 19th or early on the 20th.
Brent and Dixie