we don't use a towel rack per se...we use large "3M Command Hooks" that are available in brushed nickel that matches the rest of the hardware in the FunFinder. We also use the Command Hook refill strips to mount things like toilet paper holders, television signal strength meter, clock, etc. and other wall mounted items. Great things...they hold like construction adhesive, but, release without leaving marks on the items or walls when you need to move something.
I'm not sure what you consider "light" in medicine cabinets, but, the "heavy duty" Command strips are rated at 5lbs per strip...a series of 4 across the top and 3 or 4 on the bottom would support 20-30 lbs without drilling into the walls or worrying about hitting wall studs. Since the weight is a vertical shear force, the paneling alone should be adequate to support the weight. The heaviest load we have on a Command strip is the dirty clothes bag...it hangs on a single 5lb large Command Hook on the back wall above the bathtub (the cat's litter box). It gets much heavier than 5lbs and has to take the most sever bouncing (being on the back wall) and it hasn't loosened or budged in almost 30,000 miles of travel.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)