The remoting jar is over 200K as it is now, so is larger than what you are wanting. However, this includes a lot of extras that you probably would not need (callback persistence, samples, etc.). My goal is to break up the different parts of remoting into core framework and then different implementations that plug in (each being their own jar), but probably won't be able to do this till end of summer.
However, remoting does have support for http(s), including proxy and basic authentication support. If can live with the remoting jar size for now (or feel comfortable removing the classes you will not need), it should be fine for applets.