Jeremy, thanks for the thanks!
It was a pleasure meeting you, and I am glad that I could help you solve that rewrite thing.
Upon reflecting, I think that the escaping backslash is only needed on the capturing side, not the rewrite side, so this rule

RewriteRule (wp\/?)$ \/ [R=301,L]

may become this one

RewriteRule (wp\/?)$ / [R=301,L]

Upon further reflecting I think the escaping backshlash is not needed at all when in .htaccess rewrites - it usually is needed in regular expressions where the "boundaries" of the expression have to be set, which usually is a forward slash. "/^(.*)$/" for example.
In .htaccess rewrites those boundary chars are not needed, so a forward slash I think can be used un-escaped:

RewriteRule (wp/?)$ / [R=301,L]