Now that we're in the lovely times of needing to check bags, the 45 minutes could be pushing it.

Fortunately, DEN isn't an ORD...so traffic holding patterns and such shouldn't slow your flight down, but it is a huge airport so even if you take off from SEA 10 minutes late, that only allows ~30 minutes connection time. Probably enough for you, but no guarantees for your bags.

The RCCs at DEN are mirror images of each other.