I had 2 tow vehicles with a hitch from a Canadian company with manual slide rails, don't know if they were available in the USA. Can't think of the company name at the moment , but I will.
There is a 5er hitch that mounts, in the bed by locking down to the goose neck ball, have you considered one of those?
Company name was Hi-Jacker, I'll see if they're still in business and marketing in the USA.
BTW: a belated Welcome to iRV2 , first post I see.
EDIT: Found info , company bought out by Demco, but still marketed under the Hijacker name . For some reason my Nortons considered Demco site unsafe??
But I found this.