most of my attempts were all trying to join them by some kind of boxed type piece between them..... well haha that crap didn't work! everything I did allowed light in, to make a long story short, just join your sections at a spot where 1 of the sections is flat, pull back a piece of your wall and slide the other section up to it, remember to highlight the piece or pieces you want your section to join to first then highlight the other 1 and weld them....at the top where the curve is, draw a brush approx 2 to 3 grid and use your E key and angle the side upward like at a 45 degree angle and slide it down on top of your main piece, widen and lengthen it as you need to block out light, compile and test it until you get what you want.
I did it this way and it worked, I run or walk through it with no problem, its just not as pretty as I would have liked it to be, BUT, it works!
Cheers