The minimum recommendations for a door width to accomodate a wheel chair is 32 inches or 36 inches if a turn is needed. I've also read that a wheelchair's width is between 24 and 27 inches at the wheels, but one would have to worry about hub clearance, hand clearance therefore extra inches for the doorway are needed.
The Montana doors are less than what's recommended. I just measured my '06 3500RL Montana and the widest door distance is 28 inches because of the lip that the door closes against and 29.5 inches without the lip. The other problem is there are also two steps into the rig that will need a steep ramp. Their are rigs where the exterior stairs lead right up to the door and there is no drop down in the entryway but I don't know if your rig is set up this way.
I have seen 5ers with ramps leading up to the door, however I don't know the details of how they solved their accessibility problem of if and how the door was changed.
I did a quick internet search and found this link:
http://www.rvlifemag.com/file346/allaccess346.html
In the middle of that page there is a statement in bold "For more information on making your RV wheelchair-accessible, contact the Handicapped Travel Club at 714-524-2700 or visit www.handicappedtravelclub.com". This link has much more information including "Links" to other websites with more information.
The point is that there can be many ways to answer your questions for preparing your Monty permanently or temporarily. I hope you let us know what you decide, whatever it is.
God Bless you, we wish you a speedy recovery and may your future travels be the best!