If your WLA model does not have an E-Track system (or some other brand), I would recommend paying the $150ish bucks and installing one. It's quick, painless, and self-explanatory... and will save you hours of hassle (and potentially a dented tank). It has the added option of a wheel chock snap in that makes the space useable when not hauling a bike. Boltiton also has a nice product, just ensure you order the right length crossbar for your application.
I've used E-Track systems on my cargo trailers for years and have had nothing but success (no dented tanks on my 1958 Duo Glide).
As far as where to drill, I'd consult your service department for a set of plans on your RV that detail where your pipes / electric are located. Every RV is different so unless someone comes on with a schematic, not sure many folks will be able to give you definitive answers that won't potentially result in a leaky pipe.
Best of luck with the new ride.