Redgard is a good product, have you read the installation instructions? They are fairly detailed.
You really do need a sloped bed and a preslope, though for the pan.
The hardest part of the install is ensuring you have the prescribed thickness without voids or bubbles.
There are surface applied membranes that work well, too. www.schluter.com makes Kerdi, which may be eaiser in some ways, and is maybe less prone to install errors. Noble makes some that work well, too.