Wrapping should have no affect on verification. Email of course MUST send with CR+LF. But if you are on some version of 'Nix that gets translated to just a LF on receipt, or the LF -> CR+LF when sending. If you are on Windows or OpenVMS that would continue to be CR+LF. But verification is supposed to toss out both CR and LF characters in doing the signing and verifying. If you want the WebMail that is the worst in how wrapping of things is done, that has to be Yahoo. I have done extensive tests of the signing problem and they are available in the following file:
http://www.securemecca.com/FireGPG.zip
In short signing of WebMail messages with FireGPG is a big problem and generally speaking, making yourself GMail-centric is bound to blind you to what is going wrong. The common format that all Mail User Agents have is plain ASCII text. Actually, that is all that is sent anyway, and MIME markings will occur for anything that is not in that format. Further, if youhave only LF in your ASCII text they must be converted to CR+LF before they are sent down the pipeline. I am talking about the actual transport. It really helps to have POP mail since you can save the message to a file (don't do decryption in the MUA) and you can see all the MIME markings (but the text that was sent is always ASCII with CR+LF line endings with the MIME markings around the various pieces). With WebMail what you see and what is may be worlds apart. I tried saving the entire mess in Yahoo, and at the time that confused rather than enlightened me.
What you want though is not just a GMail-centric thing. You want somebody on the other end to be able to verify a message whether they are using GMail, Yahoo WebMail, HotMail, AOL/Netscape, or a POP or IMAP mail account. BTW, you can transform your GMail into a POP server if so desired.
If that requires plain text so be it - that is the best choice.