I have my Honda 2KW in the bed of my truck sitting secured in the tailgate corner. When I need to use it I just pull it our onto the dropped tail gate...
Mine is secured to the inside tie handles. I also have the folding HARD plastic folding panels bed cover made by FOLD-A COVER.
Been doing this since 2008 and so far no problems with security. I am totaling relying on OUT-OF-SITE-OUT-OF-MIND...
Roy;s image
My trailer is a pull trailer with trailer hitch but if I had a fifth wheel I would be looking at something like this for my truck bed. This too can be covered with the FOLD-A-COVER truck bed cover when not towing the trailer... All is locked up out of sight when not towing. The folding panels will stack up behind the truck rear window area when you are towing...
google image
This is a better view of the FOLD-A-COVER
Google image
Roy Ken