Hey, wheel chocks are cheap! Harbor Freight has them on special from time to time.
You can also bend a piece of rebar to meet the width of your wheel & weld a pair of straps to the underside w/mounting holes. Using a gas ax to get it malleable 1st & a big piece of pipe as a mandrel for your bends would be best if you want the home-grown variety.
I just bought a Moose & a Pingel, on-sale & use a <5' w. trailer.
My last trailer was great, 13" wheels, aluminum diamond-plate deck, Pingel chock. Evidently someone else thought so too, as it was stolen from my yard (yes, it was secured). I made it from a Rocket boat trailer.
Word of advice, check the load rating of your straps, many are barely suitable for the job. Think to yourself-"is this a piece of equipment on which I want to cheap-out? How much damage will it do if the bike falls-off or topples?"