I am not sure you will find any chock that doesn't have to be bolted to the floor. Your main issue is that the underside is covered with heavy plastic and you will need to get around the plastic to hold the nuts underneath. I would get one that you can drive up into and it grabs the front wheel. I bought a CHEAP version (maybe Harbor Freight?) and it didn't work worth a darn; never could get it adjusted properly for my bike. I would go with a better one such as the Black Widow:
https://www.discountramps.com/black-...CABEgKQ2vD_BwE
They must give you tie down hooks so get some of those fuzzy covers for your straps else you will scratch something. Make sure you pull the front shocks down compressed enough where the bike won't bounce.
It's your trailer; who care what Keystone or the dealer says regarding bolting to the floor; just make sure you use stout good grade bolts/nuts and I would use nylon insert nuts so they don't loosen as you don't want to crawl under the trailer more than you have to. You will also want to investigate something to decrease the angle of the ramp as your Harleys WILL drag going over the ramp pivot joint. You can built a little ramp step to raise your ramp about 4 or 5" and something the bike will be able to get up onto. I had a Black Widow 3 piece ramp with the big curve in it I carried and just tossed it on the ramp so my bike or trike wouldn't rub where the ramp door hinged. You can also find a place where you can park for a minute with the vehicle pointed downhill so the ramp is more level and that will work and some folks raise the front of their fiver for unloading to get the bikes off and that will work.