I don't think it's been stressed clearly enough that the total weight isn't the issue, it's how far back it is! The truck's total weight rating isn't the question here.
With such a short ashtray, uh, I mean truck bed, your truck will be loading like a seesaw, you'll be adding top heavy weight to the rear and taking weight OFF the front! That's what the handling issue is. If I were you I'd get a small trailer and not a truck camper.
Then there's the fact it's an old and likely rotted camper that you're badly overpaying for!
Having said all that... yes your Toyota will carry that camper. You gotta start somewhere. I had mismatched and overloaded truck/camper combos when I was younger. They worked and I lived to tell about it. I'm just tellling you, it won't be right and you'll want something better matched.
