Used TT buying checklist

Thanks for the advice about the flashlight. Time will tell about returning to pop-ups. They'd probably be ok during the summer in Washington and especially Eastern Washington. We're moving from northern California so I know we're in for colder, wetter weather up in Whatcom County. Generally it isn't much colder or wetter than where we are now, but it can get down below 20 once in a while.
Our Ford Ranger isn't designed for a larger TT and I have no plans on getting a big truck, so this is why I expect to be selling the TT.
Can you actually walk on the roof of a TT safely? ( no foot through the roof )