For the toilet paper holder it might be better to mount under a shelf or on the side of a cabinet. In our case we got a toilet paper holder that sits on the floor. Mount your towel holder to the back of the door, just remember they are hollow core doors and you may want to use blind nuts/mollys since the wood thickness is only about 1/4". For us we used a towel holder that hangs on the top of the door. Otherwise you need to find a wall stud which depending on the manufacturer may be either aluminum or wood. They may say studs are on 16" centers or such but don't depend on that, it may be 16"'s in one place and 20" in another or 15" in another. They don't really space them equally in an entire wall. Also, don't use long screws in a wall as they are only about 2 1/2" thick overall or less.
2014 Palomino Puma 25RS
2011 F-150 Super Crew XLT
Days camped in 2014 - 23
Camped 2015 - 47
Camped 2016 - 51 done - 6 more planned so far