This procedure is well supported and recommended under the latest FreeBSD releases and is documented in the Building and Installing a Custom Kernel chapter of the FreeBSD Handbook.
This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.
For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.