Directly from the RPM Website: [NOTE: They talk about Monster trucks but this will work for anything]
"Toe angles can be checked using the same RPM Camber Gauge. We do not recommend using the RPM Toe-In gauge to check large tire diameters because the gauge cannot reach the centerline of the wheel, which would result in inaccurate results. To use the RPM Camber Gauge to check toe angles, all you have to do is have a 2" x 4" block of wood or other square object handy to rest your wheels against (be sure that there is clearance around the bumper and skid plate areas in the wood).
To check front toe angles, turn on your transmitter and receiver and allow your steering servo to come to rest. Leave the transmitter and receiver on while checking your front wheel toe angles. Bump your wheels equally against the block of wood (check to be sure that only the tires are hitting), then place the base of the gauge horizontally across the face of the tire and place the gauge edge against your block of wood. The reading on the gauge is your toe angle for that one side. Please remember that this angle, plus the angle of your second wheel, will be your total toe angle. Once you adjust in your front toe angle, run the truck and use your steering trim on your transmitter to adjust straight line tracking.
Rear wheel toe is done identically to the front except you do not have the convenience of a transmitter to adjust straight line tracking. Unfortunately, there currently is not an accurate way of checking rear wheel toe angles in relation to the chassis. The best method to get an accurate rear toe angle is to measure the length of your toe links. Once you are sure both rear toe links are identical in length, make sure toe angle adjustments are made equally between sides.
For front wheels, a negative reading on the gauge represents toe out, while a positive reading represents toe in. For rear wheels, a negative reading on the gauge represents rear wheel toe in. An excellent starting point for most large tire trucks is approximately 1/2 degree of toe in per side for both front & rear wheels. "
before all the tweak stations, this is the way I always did it.