Oops, sorry, I thought you were encountering it when building your application code. Indeed, try and find out which package it’s in, then put the excludeModule into the definitions in the panda3d.pdef or thirdparty.pdef file. Or just put it in all of them if you don’t know. You should be able to see in the build log which package it was building last, though, right?
The --host should be a URL pointing to the directory containing the contents.xml, which will be “built_thaumaturge/stage” by default. Note that this should be a file:/// URL.
The _rt is for appended for the runtime build. You don’t strictly need to build your own runtime, other than to get a version of the runtime that defaults to the host you specify, but the host location of the “panda3d” package is determined from the package requirement specification in the .p3d file.
On a sidenote, the new deploy-ng system that is intended to replace the rtdist path is becoming increasingly stable, so at some point it may become less effort to get it to work the way you want than the old rtdist system.