The t-, f- and p- helps vRewrite tells which is which. There's really no other way to accomplish this without changing a good majority of the script.
As far as newpost is concerned, that part doesn't have a problems as you will get redirected back to the t- (not the p- mind ya

). SEOs really doesn't see this as duplicate content.
As far as the reply URL is concerned, make sure you have vRewrite Redirects enabled.