Kevin,
bknr makes use of the iconv package that is in the thirdparty/ tree. The original iconv that is linked from cliki.net contained several bugs that I fixed. I would not try to use bknr with random packages installed from the net and use the thirdparty/ versions instead.
I am aware that the dependency on a private thirdparty tree is not nice, but it has the advantage of keeping the system maintainable without having to keep up with all the new versions of third party packages that keep coming up. The additional disk space requirements set aside, I don´t think that this requirement is a significant burden unless one needs features of a newer version of a thirdparty library included with bknr.
I am planning to factor out the datastore components this year and make them asdf installable. An sbcl port is on my todo list as well, but without a concrete project, this todo list shares my attention with the several other free-time activities I have.
-Hans