If I were going to buy a tent for fishing I think I'd go for something like a single skin, two crossover pole style. I have three or four that meet that description and I'd happily use any of them in almost any weather. You can set them up in minutes using no guy lines in moderately settled weather. Some 'festival' tents are like that. You can get them for a fiver if you look in the right places at the right times. One of mine was a fiver.
Condensation is usually much more of an issue in a single skin tent. I take a couple of face flannels and wipe it off. I'd take a sleeping bag as well as a bivi bag.
There's a fantastic thing like a bivi/sleeping bag posted somewhere on here, I think MartinK9 first mentioned it as one of his wants; Maybe he'll chime in before I find it, turning in now...