Gentoo respect the FHS policy, and I think almost all linux distributions. When installing gwc on gentoo, I get the following warning:
The main issue is than gwc build system don't understand standard configure parameters like --docdir=/usr/share/doc/gwc-0.22.06 or --htmldir=/usr/share/doc/gwc-0.22.06/html
Patches are welcome. Or (preferably) pull requests against the stable branch at https://github.com/alisterh/gwc
Otherwise I'm not likely to look at this in the foreseeable future, due to other commitments, sorry.