I wouldn't install a paper towel holder. We had one, mounted under a kitchen cabinet, and it pulled out after just a couple of months of use. DH wanted to reinstall it, but it certainly seemed to me like it was just going to happen again -- that wood was very (very!) thin. So I bought one of those upright paper towel holders that just stands on the counter-top, and it's tucked into a cabinet when we're rolling.
With the TP holder, DH never got around to installing it, and then I found a hook at Walmart that's sold as an over-the-tank TP hook for a spare roll (for home use). In our TT it hooks over a lower cabinet door that's right next to the loo. Perfect solution. It also is stowed in a cabinet when we're rolling.
I guess I haven't installed any of the 3 items you mentioned. For towel bars, I've got some over-the-door hooks that hang over the top of the shower enclosure. We hang lots of things on those -- PJ's & bathrobes to name a few. And oh yeah, towels.
IMHO, screwing anything into the wall, that's going to get some wear & tear on it, is just asking for trouble.