Is a manual slider that much trouble?

[Notanlines]

"If you have a newer trailer with the corners rounded you probably won't even need a slider"
I'm afraid this is a blanket statement that requires a little more info and thought. There are thousands of repairs made every year to rear windows and truck cab corners because the owner thought the 'rounded corners' were the answer.
You will not know how sharp you can turn until you actually buy an RV and give it a try. Anyone who says they can tell you with the info you provided is simply wrong. There are many more variables than you mentioned.