My first RV trip in 1996 had our 2 bicycles on a bike rack on the rear bumper and we left Ontario on Dec 27th in a snow storm. I didn't think any more about the bikes until a week later when I went to take them off the rack in Florida. I couldn't believe the mess they were in (no bike cover) and we ended up throwing them away after the trip as they were rusted and salt-correded so badly. Since then I've always carried them INSIDE the trailer.
Our next trailer was a large 5th wheel so they easily went in the basement, but with the FR Grand Surveyor I found it worked well to carry them on the "collapsed" dinette. I made a plywood board about 3'x2' with two dummy axles on the top and non-skid sheet on the underside. Removed the front wheels and bolted the bikes onto the dummy front axles and bungeed the front wheels between the bikes. We did about 60,000 Kms with this setup and no problems.
When I got the Lacrosse recently, I was going to add a hitch mounted rack (as there's no dinette, only a free-standing table) but I was concerned about the long term structural stability. What I found I can do is to use the same idea of a non-skid board to hold the front forks and use a board between the sofa and the table, and one between the table and the slide wall. With PT's "Oversized MAX Living Room Slide Out" there's more than enough rome to do this
. It's a bit inconvenient when you're travelling but we tend to use restaurants rather than eat in the trailer while towing, so it works for us.