Kevan, I have psoriasis and had RT ending last Nov. There were no adverse problems with affecting it or making it any worse, I do not have a large area like you but still get it where yours is. I have been using Double base gel for about three years and it is very good at stopping the itching. I often apply it twice daily for about three or four days then stay itch free for a week then have to use it again.
When you do the daily driving make sure you know where there are loo stops on the way ( I found every ten/ fifteen minutes was normal) take a container with you or get your GP to prescribe a URIBAG which will take several wee's at a time and is seelable.
Best of luck with the RT, you will make some new friends in the waiting area as most people had a regular time slot so you will see the same faces daily.
Regards Chris/Woody
Life seems different upside down, take another viewpoint