To answer the initial question.
I went through a boat build nearly two years ago and got hold of the RCD docs via the RYA, and yes you do have to pay for that privilege. However, you will need to have the RCD docs approved via an authorised agency and the RYA will do that for you.
If you follow the RCD route then you should not have any further probs in the future and will have some comfort that your boat has been built to current standards. The BSS is very basic in comparison.
Yes it is possible for an intelligent layman to follow the RCD docs, even though some may require several readings to get to the nitty gritty.
At the end of the day it is up to the individual boat builder to go down the route he or she feels most comfortable with, however the legislation is clear that if you intend to sell the boat within 5 years, then it should be RCD compliant.
Best of luck
paul