We are leaving for Florida tomorrow and going through Charleston on 17 pulling a 19'TT.
I drive that route all the time going to Jax Fl. Probably driven it 20 times at least in the last few years. Have only done one round trip with my TT. I have never taken 526, so I guess I can't say which is best. I just like driving through town. I normally avoid arriving at rush hour. Traffic was slow when they were working on 17 N of town, but I think all that is done now. I think they are also finished or very close to finish on 17 S of Charleston.
I may try 526 tomorrow just to see the difference. I never even thought about not going through town on 17 with the TT. Of course my TT is only 19' and I have driven the route many times.
Where you turn to Folly Beach there are some large trees close but not many, and I don't recall them being that low, don't know where you would run into trees. I think if I had a really big rig, tall or not, I would play it safe and go around. The route through town is well marked. Got to cross the big bridge, beautiful view, but it does have a grade.