Don't listen to these negative Nancies!
I have direct experience using an older version of the same boat (probably the Mariner 4 that FlyingDutchman is referring to) and I think for what you intend to use it for, you'll be just fine. I have even run this boat with two people paddling into a couple of class III rapids and while it help up fine, I would say that this is past the boats confidence range. We took on A LOT of water in those rapids and needed to pull over to bail. My opinion is that this boat is pretty resilient, and I'm not sure if yours has an inflatable keel, but mine did and it made it track really well. II to II+ is just fine for this boat.
I used mine for day trips and multiple overnighters... everything up to class II+ rivers, up to 4 day/3 night trips, with two people and all their gear on the boat (and more beer than you can shake a stick at) and I thought be boat handled all of that fine.
A few tips to share from my experience:
1) I glued some thin wear strips on the top of my tubes to prevent frame wear. I used a pretty heavy-duty fabric, but if I had it to do over again I'd just use this thinner IK material that's softer and easier to work with (AIRE PVC Kayak Material at nrs.com
2) I agree that ideally a frame would go outside the stock plastic oar-lock parts that are welded on the boat, but I put mine inside those locks as well and didn't have any issues. When I was lining things up, it didn't look like outside those locks was going to work.
3) I had very low clearance between the oars and my legs... you might need taller towers and slightly longer oars than you think. I had either 6.5' for 7' cheap wood oars and the regular 6" NRS towers.
4) The boat isn't self bailing the the space between the rigid floor and the extended keel has a propensity to fill up with water. I cut a small oval out of the PVC sleeve that holds the rigid slats to allow space for a manual bilge pump to fit in, pointed towards the lowest point in the keel section... this allows easy bailing of any water that makes it's way over the sides.
5) I removed most of the perimeter line and only left short sections on the bow and stern for something to grab on to. As you can see from my pics, I attached the frame with 8 straps (vs 4 on large boats with full sized D-rings) to distribute the load amongst the welded on attachment points. I didn't reef on the straps, but it was pretty tight on there and didn't feel like I was in danger of ripping them off.
6) Because it has a rigid floor and just rested the cooler on that floor and used a couple of straps to attach the cooler handles to the frame rails.
I have since upgraded to an RMR so I can carry more gear and push the difficulty levels, but I have absolutely no regrets with my Intex boat purchase and have a lot of fond memories of the rivers I paddled on it.