Leaving it unattended (unhitched), really not a good idea anywhere.
Depending upon where you go, there is almost always somewhere you can park (some West Coast Cities are real sticklers though from what I've heard.
Basically, for us travel trailer owners, I think most of us park the camper in a campsite nearest the attraction we want to see and do. Then the tow vehicle can go anywhere and the camper is safe.
If you visit major attractions (like ball parks, theme parks, stuff like that), they always have overflow parking for large vehicles. If you are in a smaller town, you may find a church you could park the camper in (but I still would not want to unhitch). If anyone is at the church, very few church groups will give you a hard time for just parking a few hours, especially if its not their service time.
Another thing, you may not be able to park the entire rig on the main drag, but if you go off the main drag a block or two, you can usually find on-street parking as long as you are not over-nighting. Then you can walk to your intended site.
Basically, it really is just a matter of using your head. We have always been able to find somewhere to park without unhitching so we can visit or go eat when passing through different places. And my camper is 35.5 feet long. With truck and cargo carrier on the trailer, I'm 59.5 feet long. Never had a problem finding somewhere to park the monster!
