Your all forgetting that Cas will be in exactly the same boat, and infact will have it tougher, as they will have a long tiring coach journey prior to the game and will be facing an hostile away crowd.
I personally expect Royce to rotate some of the forwards. For example i see no reason why the likes of Hale and Dixon and Ashurst cant form the starting backrow. Two of these three players will be fresh.
I would look to rotate the props heavily, so would start with Graham and LMS but have TP and Mcgennis on the bench.
The backs shouldnt really be that beaten up compared to the forwards, so they should be able to handle another 80 minute slot. Though i must say I suspect Jonny Lomax may get rotated at some point.
Overall i think the team could look something like the following
Makinson
Gardner
Shenton
Meli
Foster
Moore
Lomax
Graham
Roby
LMS
Hale
Ashurst
Dixon
bench: TP, Mcgennis, Wilkin, Armstrong
He might not even play Armstrong on the bench, preferring instead a forward to help ease the burden of the forwards battered bodies. Hence Soliola could be the fourth bench spot.
I think these monday games are as much about fatigue management as anything else.
You need some fresh guys to take the heavy burden while rotating the big guns as much as possible to limit their fatigue levels.