So, I've had a Big Agnes 3p for 5 years now. It gets moderate use for not-terribly-weight-conscious canoe/bike/car-camping trips and the occasional 3-person backpacking trips. I don't use a footprint, but I do make sure my sites are pretty tent-friendly (grass/dirt/pine beds). Though I haven't had any problems in the past, the last backpacking trip I took the tent on had one long night of pretty heavy rain, and the tent collected an inch or two of standing water by morning.
We were at full capacity for the evening, so the bathtub floor was stretched out as far as it would go. The fly was taut, but we started having water leak in through the side of the bathtub floor – a couple inches off the ground. (The floor itself was dry to start, the mesh above the floor wasn't in contact with the fly, and we didn't really have a condensation problem inside the fly until early the next morning.) As soon as we noticed that water was beading through the side of the bathtub floor, we guyed out the bottom of the fly to get it as far away from the tent as possible. Water continued dripping in through the side of the bathtub and gathered along the floor of the tent and on all the clothes/sleeping bags that touched the wall of the tent.
This was our last night out (and a warm summer weekend), so we weren't screwed, but I'm now nervous about taking the tent out for more trips. Initially, I figured this was human error, but after we readjusted the fly, there was still a major problem. Any of ya'll have any insight as to what the problem might be? Is the tent just getting past it's usable life? Would those waterproofing sprays fix the problem? Am I just really, really bad at setting my tent up? (If it makes a difference, I've never had a similar problem in any of my other tents – including a 2-person double wall that gets more use and is going on 9 years now.)
Sorry for the length, thanks for your help!

