A pop-up doesn't necessary mean lighter weight. And when looking, remember the advertised weight is for a unit without options.
Reason folks like a cassette toilet is though it has smaller capacity, it is easier to dump. You can grab the cassette and dump in a regular toilet, pit toilet (check regs), or at the regular dump station.
If you plan on off-road, try to stay with a non-basement style camper to keep the cog as low as possible.
I have a Lance 815 which is a bit tight in the shower but a nice hardside for off-road because most of it's weight is down low, it is about the shortest hard side, and only 83" wide which is a foot narrower than a lot of TCs. The 815 works on long and by adding two rear skirts short bed trucks. Loaded for a long trip, we are only at 2,400# which should be a good match. Even the older units are in good shape and can be found relatively easy.
Now that the kids no longer camp with us, we really love just running around with it. Because it is narrow and doesn't hang over the back of my long bed truck, we can park in a standard parking space. In some national parks, we are even allowed to use tent sites because as they see it we use the same parking spot. This opens up a lot more site options.