Recent updates to iOS 9 - specifically pertaining to changes in the Safari browser - have made it such that Safari will not allow users to remain logged into password secured sites for an extended period of time.
In light of these changes -- which are not modifiable, this support article details how to enable the storing of passwords in Safari. Following these steps will allow you to easily log into ServiceTrade's Tablet Mode, after Safari has forced the initial login session to expire.
First, go to your device's Settings.
Then, select Safari from the left-side menu, and proceed to select AutoFill from the menu on the right (shown below).
In the AutoFill menu, ensure that the Names and Passwords toggle is switched 'ON'.
Once you have turned on AutoFill for Names and Passwords, Safari will start asking if you'd like to save your login credentials for future use, anytime you login to a new website.
Now, the next time you go to Tablet Mode and have to enter your username and password (after updating the settings detailed above), Safari will present you with the option to save these credentials for future use.
When you get this prompt, select the option to have Safari save your login credentials. Now the next time you go to Tablet Mode and Safari has logged you out, your login information will already be autofilled. So all you have to do is tap 'Login' and you will be automatically logged in!