Josh, just to be sure you know...
You only really need to do a backup once. Once you have created your safe slot for your custom ROM and installed it, you can easily switch between the two at bootup by choosing which one you want to use within safestrap. There is no need to re install your backup just to go back t the stock ROM. Essentially with safestrap, you are creating a multibooot environment where you can choose between which ROM you want to use.
EDIT: just to be safe, I would recommend switching ROMS without webtop active and just do it through the phone only.
David