Mid-May is early for crossing the high Colorado passes. I'd suggest just taking I-25 to I-40 to Williams, AZ.
However, if you watch the weather forecasts when you're ready to take off from Colorado Springs you could do I-25 south to 160 west and the only place to really watch out for would be Wolf Creek Pass coming into Pagosa Springs, CO. If it's clear you would have no issues driving it with your motorhome. If not, perhaps lay over a day or two in South Fork until they get the highway clear and then go for it.
From Pagosa you'd stay on 160 into Arizona at Tuba City and Hwy 89. Have you been to Mesa Verde Nat'l Park, CO? You could stop there. Even if you don't tour the park, this would be a good stop before continuing on 160 - either here or Cortez, CO are some RV parks. Then continue on 160 to 89. Then take 89 south and if you want you could pick up Hwy 64 west at Cameron into Grand Canyon Nat'l Park. It's 275 miles from Mesa Verde to Grand Canyon via Cameron, AZ. Stop at Trailer Village in the park and just see if they have a spot for you. There are always cancellations.
If no spot, continue on 64 south to Williams.
Or from Tuba City and Hwy 89, stay on 89 into Flagstaff and west on I-40 to Williams.
Full-timed for 16 Years
. . . Back in S&B Again
Traveled in a 2004 Newmar Dutch Star 40' Diesel