Personally, I do use a mail service to receive all my mail and send it to me wherever I am when I ask for it. I have been doing this since 2005 and it has worked well most of the time. On rare occasions, I do get a postmaster who threatens to stop accepting general delivery. Educate them by showing them the manual and/or going over their heads, move on, or accept being bullied. Your choice.
For anyone using General Delivery for mail and getting told by a Postmaster that they can only use it for 30 days, apparently several postmasters have been misreading the DMM (Domestic Mail Manual). The manual has been updated to make it clearer that the 30 days only applies to how long they will hold an individual mail piece and not how long you may use the service which has no limit. While General Delivery is meant to be a temporary service, they do understand the need for transients and those without a formal mailing address to receive mail per an update notice published by the USPO and current section 6.0 of the DMM.