If you have a gap between the floor pan and shower wall, do what Gritz suggests for the leak. If there's no gap, you'll trap moisture behind the wall and you know where that leads to. You may not thing much of it, but water bounces off you in the shower. Your head, your shoulders, etc. If it gets high enough, it'll run down that wall and cause damage. A quick bead of silicone is not going to hurt anything if you have that gap ay the bottom and if that's not the problem, you still haven't done yourself any harm. Have a spray bottle with water handy. Run the bead and spray it, then run your finger over it. It'll create an acceptable look.
Your mileage will drop with a towed. You probably know that too. Pick something light; I tow a 3500 lb'er with a v10. 18k miles and 7.3 mpg. Not the best. The shift points you mentioned seem to be a vast improvement over the v10. It may change with a towed.