As long as it is the black or shower tank, this isn't that tough. Drop the coroplast at the rear of the drop down frame. It only takes a couple of feet to access the valves.
Here are some links to those who have gone before you with this problem. Search is your friend.
https://www.montanaowners.com/forums...ad.php?t=77401
https://www.montanaowners.com/forums...ad.php?t=77720
https://www.montanaowners.com/forums...ad.php?t=76577