Hi Peter,
I can't really help you on the specifics of RP as I have only ever had RT & HT, I guess your doctors/nurses should be able to advise?
However once the immediate effects of the RP are over I suggest you should walk just as far as you ever did.
My Consultant encourages his patients to do lots of physical exercise before, during and after RT, aparently it minimises the side effects.
I have a mate who had RP and we both go out walking together quite often, we did 10 miles last Wednesday, including a pub and some al fresco toilet breaks.
Like you, following RT I was initially quite concerned not to overload my bladder and/or embarass myself in public. However after a few months I developed a sort of devil may care attitude. Long term you have two choices, either you can arrange your life around toilet breaks, or you can start to stretch things out and see how long your baldder can hold out. I mean if the worst comes to the worst you have an excuse, you have PCa, and most shops and offices will let you use their facilities in an emergency.
:)
Dave